There are very few ways you can insult someone without throwing a whole group of people under the bus that don't deserve it.

This notion that they would have to "deserve it" basically means that the only valid and unproblematic insults are ones targeting moral character - "jerk", "asshole", etc. Maybe more nuanced character flaws like "willfully ignorant".

But even these could arguably be made problematic by recognizing that a person's agency over their own behavior is limited. Sometimes a person is an asshole due to a trauma response, or willfully ignorant because they've inadvertently built their self-worth on a falsehood.

Basically what I'm saying is you should be kind to people. It's difficult to carve out exceptions to this without creating the ideological basis for an injustice of some kind or another.

(There may be more important concerns in some cases than individualistic injustice. Yes, many capitalists genuinely don't understand that they're doing anything wrong. Eat the rich anyway.)