Opinions are fallible and going only on hearsay is not a good policy. But often, we don't really need to know everybody's whole story to judge some of their more questionable choices for instance when they are intentionally hurtful to other or when their choices are disruptive or the extreme case - criminal.

Of course, it's always good to keep in mind that it's impossible to know everything about another person's situation and reasoning, so reserving judgment until it's needed or clear is always a good policy. You just have to watch out if you are not too naive as I've personally have given some people the benefit of the doubt when they hadn't deserved it and that has ended up with other people close to me being hurt because of me not passing judgment and taking counter measures on time.