Each case needs to be evaluated on its own merits. If there's a lack of evidence and/or it smells, then I can't go along. It doesn't matter whether or not I like the person charged, either - fair is fair, IMO. I don't believe in joining the pitchfork brigade just because I don't like a person's politics, religion, movies, etc.
In the case of Cosby (whom I like as an entertainer), I gave him the benefit of the doubt until I couldn't any longer.