Indeed. I also think there's a distinct difference between one being stupid, and someone who is stupid; same applies to the other adjectives, IMO. I think it's how in some cultures/groups we can get away with joking by saying "Do be so stupid." it doesn't mean "You are stupid." it more means "You are being stupid.", the former being more concrete and personally, I find it very offensive, but you know, ... sure we all have moments when we are being stupid.

I think the problem with "ignorant" is that the word is so often used derogatorily, so it's kind of a gamble as to whether you would offend someone by using it innocently. I said it to my dad, once, something along the lines of "ignorance is bliss" about something that totally wasn't intended to be offensive or malicious in any way, but he was really offended by it.

Another word that gets given a negative light is "pity", ... to say "I pity you", doesn't actually have to be that sarcastic, patronising meaning that we are so used to hearing, but alas, we're all so used to it being that way; it is actually a very nice, heartfelt thing to say - and I quote: "the feeling of sorrow and compassion caused by the sufferings and misfortunes of others." Interesting, really, I think.