I will say this, Rosie. As a rule "assume makes an ASS out of U and Me." But if we couldn't use that tool at all, we would be totally clueless.
It relies on a part of you that can discern truth from nonsense, it relies on a part of you knowing that being judgmental out of hand never proves anything; and it also relies on your having the proper information that probably is a fact. I can assume that Trump is a total waste of space because I have a lot of information on hand to verify my assumption.