I'm going with the definition of the word as described by Oxford, Cambridge and Merriam-Webster. You're trying to use something else which is currently unspecified.
In particular, our disagreement appears to stem from the fact that you (needlessly, in my view) restrict the definition of authoritarian beliefs to require an underlying regime and/or the need for enforcement of authority. The words doesn't necessarily mean that, and any belief that others should submit to a particular group's views are generally authoritarian regardless of their power to actually realise those beliefs.
I do believe you're misusing the word here, but at least now I understand why you'd disagree with my assessment.
I would tend to agree with you in another context, like literature, where authoritarian can have a looser definition for the purposes of narrative and metaphor.
1 In the context of public policy, however, I think your definition is much too broad to be of any practical use. If we don't include in the definition the use of force to achieve compliance of obedience to a viewpoint, then any and every "ought" claim is authoritarian by definition. All of ethics and all of public policy is authoritarian on your view because they all assert actions and behaviors that some or all people "should" do. I think it's important to be able to differentiate between "Actor x should (voluntarily) choose action y," and "Actor x should be forced to choose action y." I think that this distinction literally is the difference between libertarianism and authoritarianism. I think you've demonstrated more examples of libertarian feminism than authoritarianism.
Here are some examples of what I mean:
http://kotaku.com/stop-preordering-video-games-1713802537 This article expresses the belief that others (people who like preordering video games) should submit to his viewpoint of not preordering video games. And he's definitely aligning himself as a member of the group of people who decry early release/preorders/shitty video game sales practices/etc. "But when it comes down to it, preorders suck. They’re a shitty practice, and they exist not to serve you, but to serve the people who sell video games. Participating in a shitty practice helps propagate that shitty practice. So stop participating." Is this an authoritarian position?
When Parsifal tells me in IRC that I should ditch Windows and use OpenBSD, is he being authoritarian? He's a member of a group of opensource enthusiasts, and he's advocating that I (voluntarily) submit to their views about the benefits of its customization, security features, and unique learning opportunities. I don't know this for a fact, but I bet Parsifal would agree that his motivation for even bringing it up is that he thinks everyone (or everyone who can) should switch to OpenBSD for their OS because [reasons]. Not by force, obviously, but voluntarily. Doesn't that make a difference?
Going back to the emoji example: how is it authoritarian to advocate for private firms (the people who create emoji) to take a private, voluntary action (make all of them black)? Is such a position really indistinguishable to you from advocating that obedience to it should be mandatory?
Most importantly, your claim that "There are some advocates of feminism who are authoritarian and should be resisted..." is then necessarily authoritarian according to your understanding of the word. Aren't you and other like-minded anti-mainstream-feminists of the belief that feminists should change their behavior according to your viewpoint? How is that not "[a] belief that others should submit to a particular group's views"?
: Favouring or enforcing strict obedience to authority at the expense of personal freedom: the transition from an authoritarian to a democratic regime
: Showing a lack of concern for the wishes or opinions of others; dictatorial: he had an authoritarian and at times belligerent manner
: expecting or requiring people to obey rules or laws
: not allowing personal freedom
: of, relating to, or favoring blind submission to authority <had authoritarian parents>
: of, relating to, or favoring a concentration of power in a leader or an elite not constitutionally responsible to the people <an authoritarian regime>
: demanding that people obey completely and refusing to allow them freedom to act as they wish: an authoritarian regime/government/ruler
You posted these as if they support your definition of "any belief that others should submit to a particular group's views are generally authoritarian regardless of their power to actually realise those beliefs." I don't think that they do. They all describe "obedience to authority," "requiring," "not allowing," "submission to authority," "power in a leader or an elite not constitutionally responsible to the people," "refusing to allow them freedom to act as they wish." To me, advocating voluntary action does not meet those definitions. "Expecting...people to obey rules..." is the closest, but it's a secondary definition, and I think it has much more value as a description of personality than public policy. All public policy involves rules, and your definitions specifically distinguishes between authoritarian and democratic regimes of making rules.
Show, don't tell. Show me those non-authoritarian opinion pieces (or whatever else you think is relevant here) by feminists. Give me links. Don't talk about how they totally exist or about how you totally already showed them to me. Just give me the links. Show. Don't tell. To clarify: I'd like to be shown and not told. I'd like to see the evidence rather than be told that it certainly exists. For the avoidance of doubt: my request here is that you show me some evidence rather than talk about how it exists.
As I've said before, I'm arguing that you haven't proven yourself right in the first place. You're the one who posted the proposition. It's as if you posted a bag of marbles in the OP and declared that you're certain that there are precisely 73 marbles in the bag, and you're sure of it because you eyeballed it. I don't need to count the marbles myself to have good reason to be skeptical of your claim. The methodological flaw is enough to make your argument unpersuasive.
That said, I'll genuinely try and oblige. You remarked that The Guardian counts as a feminist source, so I'll go on that for now. I did a search of their opinion pieces for the word "feminism" and found the following headlines on the first page of results sorted by relevance:
"Feminism is for everyone – even men and Tories: The F-word describes anyone who believes men and women are equals. It’s a shame David Cameron doesn’t get it." (literally the number one result)
"Feminism is in danger of becoming toxic: Instead of worrying about the Rosetta scientist wearing an ‘offensive’ shirt, or Dapper Laughs, or Julien Blanc, we should be tackling the root causes of inequality."
"The biggest threat to feminism? It’s not just the patriarchy: Of course, we have to combat a power structure based on male supremacy. But more insidious is ‘choice feminism’ – applying the language of liberation to dating or makeup."
"Ten things feminism has ruined for me: Bras, bikes and Thomas the Tank Engine... Emer O’Toole mourns some of life’s simpler pleasures."
"Feminists don't care if you like hot pink, eat salads or shave your crotch: There is no grand feminist overlord policing women’s personal choices. But if you need to declare yourself a “hot feminist”, you might be stuck in the past."
"'Feminism lite' is letting down the women who need it the most: I’ve hesitated to write about gender, worried that I’ll be slammed for daring to speak out. But we all benefit from gender equality, and therefore must give feminism some tough love"
"When everyone is a feminist, is anyone?: It’s suddenly cool to be a feminist. But what does that mean for feminism as a movement?"
"Why do we never worry about men's childlessness and infertility?: Older dads are more likely to have children with mental health and developmental problems. Yet they rarely face the scare tactics women do."
This looks to me a solid list of opinions from a broad range of perspectives on, by, and about feminism. Some of it is critical. Some of it is praising. Some say feminism demands and costs too much. Some of it even says that feminism isn't demanding enough. The positions are nuanced and robust. They're far from identical. I have a hard time seeing the authoritarianism in these pieces, latent or otherwise.
To me, advocating social change via voluntary action and persuasion is a libertarian methodology toward problems. It's the opposite of authoritarian, at least so far as we have a definition of authoritarian that allows us to distinguish between figures like Vladimir Lenin and Martin Luther King Jr. They both advocated for a set rules. Only one of them was an authoritarian.
1If you genuinely mean to describe feminists as authoritarian in the narrative/personality descriptor/metaphorical sense (like describing someone's personality as "bossy," for instance), then we can certainly end the discussion on agreement. It's undoubtedly true that many feminist figures in popular news media have assertive personalities that could be described in this manner.