The difference is the difference between "it may be fake" and "it is fake". "May" being the key word that makes it a meaningless observation instead of a defense. If someone wants to defend themselves against video evidence, they need to say that it's fake, and create reasonable doubt about its veracity. You don't do that with "maybe" or "could be".
> Why should it be the defendants who have to pay for the expert instead of the plaintiffs?
TL;DR: that's how our legal system works in the US, for better or worse.
EDIT: You probably don't have to attack the video as a deepfake directly, either. "That's not me, I wasn't at X, I was at Y, and here are receipts and witnesses" are highly likely to work too. Basically, an alibi.
Suppose the video isn't of an old statement made by the defendant which they don't remember making, it's a video of one of their products catching fire sourced from an anonymous YouTube account. They have no way to know if that video is fake or not, so on what basis could they claim to know for sure that it is?
But because it could very plausibly be fake, they should be able to demand proof that it isn't from the party trying to introduce it as evidence. For example, by having it authenticated by the person who created it, whose credibility could then be questioned etc.
> "That's not me, I wasn't at X, I was at Y, and here are receipts and witnesses" are highly likely to work too. Basically, an alibi.
An alibi is the defense proving that they couldn't have done it. The burden of proof is supposed to be on the plaintiff. Creating deepfakes is so easy that a plaintiff in possession of one by itself proves nothing.
> Why should it be the defendants who have to pay for the expert instead of the plaintiffs?
TL;DR: that's how our legal system works in the US, for better or worse.
EDIT: You probably don't have to attack the video as a deepfake directly, either. "That's not me, I wasn't at X, I was at Y, and here are receipts and witnesses" are highly likely to work too. Basically, an alibi.