Does avoiding a certain group of people clash with your sense of morality?

There is a long list of people who should be avoided, depending on who you ask. You might be told to avoid people with obvious childhood baggage, for example. In a recent Fluther question, a jelly asked how to teach children to avoid getting involved with “unscrupulous, mean, lying, or narcissistic people.”

I’ve been wondering whether I support that kind of advice, and I don’t. It may be more comfortable to filter your friends and acquaintances, but it seems illogical, to me. If all of humanity ignored potentially dangerous people, wouldn’t those “outcasts” become dangerous for sure?