This is a provocative question, Sven)))

So, what a terrible thing did you do, when you visited another city?

Well.... we want to say that we SHOULDN'T judge people.  But we do.  We decide every day whether we trust someone or not, we decide every day whether we fear someone or not, we decide everyday if we will help someone.  Would you invite someone into the home of your parents?  You must judge and decide.

So I  think you cannot escape the question by saying "we shouldn't".  

Nur Salaam-  I like your thoughts in particular. thanks.

Perhaps a better way to approach such an open-ended question like this is not how to judge but how to hold judgement until you're sure of their intentions. I think the best way to be a 'judge' of character is to look at the current actions of a person rather than his/her past. If they no longer associate themselves with the bad things they did in the past, and genuinely has changed for the better, then to 'judge' them by their present good character would be most appropriate in my opinion. Unless you have suffered (and may have a grudge against them) as a result of past bad actions done against you, or your community, then one would normally be more cautious.