Yes, sometimes people do use "ignorant" as an insult when they mean "stupid." Ignorant of them, isn't it?
In my understanding, to be ignorant is simply being unaware or uninformed about something. Will Rogers said, "We're all ignorant, only on different subjects." Nobody knows all there is to know about everything, and therefore I agree with him. We are all ignorant. No matter how well educated and how well informed we are, there is always something we don't know.
I'd like to define "stupid" as not capable of learning what you don't know, but that isn't fair to people with cognitive disorders. My aunt, for example, had special needs and functioned intellectually on about a third or fourth grade level, but she was definitely not stupid!
Maybe ignorant is "I don't know, and until now I have never had an opportunity to learn, but I'm listening," while stupid is "I don't know, but I'm convinced I do know, and you can't tell me anything." I have no idea how to describe someone who is incapable of learning, because actually, I'm not sure I've ever met anybody that applies to. Some people just have a more difficult time than others.
I can see why "pity" is a trigger for some people, because to pity others, you almost have to be in a position that is somehow better off than they are. It doesn't make much sense to say you pity someone when you're in the same situation they're in, or worse.
Also, it seems to me that if someone pities me, they can't at the same time admire me. You don't see someone climb an obstacle, and then say, "You poor thing; that obstacle was in your way." Instead you say, "Wow, I'm impressed. You climbed it." I'm quoting people left and right today.... I wonder who it was that said, "You can be pitiful or powerful, but not both." (looks it up) Ah. Joyce Meyer. But then there's sympathy, which might be a better word. Again in my understanding, pity says, "Nothing like that has ever been a problem for me, which makes me superior to you," while sympathy says, "Yeah, I understand. I've been there too, and could be again."