Yeah I agree with all that for the current situation but how I interpreted the other person was that even if checking was absurdly trivial he would still be against it (obviously it can't happen in real life but it's just a hypothetical). That means that they wouldn't have to "assume content infringes" and the whole YouTube problem is a moot point. It requires a different argument than the norm (as your post shows) so I was curious if that was what he was arguing and what that argument would be.