Dark matter is a hypothesis with no supporting evidence. Therefore it is an assumption. I don't care what word you choose to use to make it sound more legitimate.
What? No. If they were taking the hypothesis as true, you would be right, but they aren't. There is an active search for Dark Matter.
RET hinges on dark matter the same way FET hinges on aether.
We're not so different.
Neither one of your premises are true, therefore your conclusion is also not true.
Just as aether is a hypothesis. And aether has just as much supporting evidence as dark matter. Therefore aether is not an assumption but a serious scientific hypothesis that we are actively studying.
We can both play this game.