So we've gone from "Don't judge a book by its' cover" to 'Don't judge a book by its' content'?
How about don't judge anyone until having "walked a mile in their shoes"? Or even... "Don't judge".
Ideally, "before you judge...", you at least spend some time getting to know the person to find out a little more about who it is you're judging. And maybe that's really the issue.