And that's the point. The positive/negative claim isn't the original premise of whether or not ghosts exists. It's whether or not the evidence for them is valid.
Saying they are not valid is a positive claim. It takes on the responsibility of proof. Are the debunking videos proof? That's the issue. Not the ghosts.
Now, replace ghost with space travel. If you are denying the photographic evidence, you have a burden of proof to explain why. Are YouTube videos sufficient?
Absolutely not.
Consider the following:
Bobby: I ate a ham sandwich for dinner last night. Here is a picture of me eating a ham sandwich. Prove me wrong.
Pete: I don't have to prove you wrong at all.
*Pete walks away.*
This is a completely valid response. Completely. The burden is not then on Pete to prove that Bobby did not eat a ham sandwich for dinner. Pete does
not have to rebut Bobby's evidence.
Bobby had the positive claim. The burden of proof is still on Bobby, even if Pete walks away. Pete is completely clean of the matter.
Bobby may start gathering different ways to show that he ate a ham sandwich for dinner, and some people may be swayed by that claim, but if some people choose to walk away or doubt the evidence, then that is completely fine. At no point does it shift the burden of proof to the naysayers.
Naysayers may attempt to gather evidence that Bobby is fabricating his evidence. But the strength of their argument, whether it is poor or strong, does not shift the burden onto them.
If the Naysayers pointed out a wrapper for sliced baloney in the background of some of his photographs, and suggest that Bobby was really eating baloney sandwiches and is trying to fool people for some purpose, is the burden of proof on the naysayers to explicitly prove that the baloney wrapper wasn't there for some other innocent reason or is it the burden of Bobby to respond to those accusations?
The explicit claim always came from Bobby and his proponents, so they need to respond. The naysayers don't need to prove that the baloney wrapper was innocently placed there.
The burden of proof is always on Bobby and his proponents. Never on the skeptics. Skeptics never need to prove that "ghosts do not exist".
The moral of the story: If you are making a claim, then the burden of proof is on you.