rebdoniel –
The guy with tatoos wearing a prison uniform may be a wonderful guy too. The guy running in your direction with a knife in the middle of the night may also be a nice guy (maybe he is chasing after someone else who is about to kill someone)
The point is we judge things based on our knowledge and experience. We do it in every area of life. It is logical and the right thing to do. If we have both a theory as to why something is probable and experience and evidence to back it up its best to use that information or you might just get stabbed.