In every single societal issue, there's going to be an example that proves and an example that disproves any statement, but that doesn't mean that trends do not exist. A group of 20 people out of a million don't make a trend, but are we supposed to ignore it if 10% are acting badly? 50%? 99%?
At some point you have to admit a problem, but no matter what, in every situation "not all ____" is going to be true, and so it really is meaningless whether you're on the right side or not. "Not all _____" is never, ever going to convince anyone that their statement is wrong. It's just going to sound patronizing that you think they're that big of an idiot when no one is that dumb.
If someone is promoting a false or destructive generalization then there are other ways to argue against it, like questioning if the claim has substantial evidence behind it, or describing how destructive and counterproductive the generalization is.