no obligation to pretend we don’t see his obvious guilt
You don’t seem to get the point of presuming innocence. It is a guardrail against vigilantism. When people start making up their own minds about “obvious” guilt, it’s only a tiny step to dole out “righteous“ punishment, which, of course, it never is.
Basic rights are for everyone, not just those on your own political team.
By the way, you do have the obligation to not “see his obvious guilt”. For instance, you cannot call someone a rapist just because you feel like it. That would be slander.