I use "mong" and "retard" and I'm fully aware that it's insulting to do so, which is why I use those terms as insults. I have no idea what context the people who are claiming to be unaware of their insulting nature use these terms in, but I guess that if it's anything other than as an insult, then they must talk like a bit of a mong.
My rough logic for insults is like this:
To call a person with no mental or physical deficiencies a "mong", a "retard", a "sp**", or similar, is a criticism of their behaviour and not necessarily an insult to anyone afflicted by any of the things related to those terms. You are saying that their behaviour is deficient compared to what you'd expect in the same way that you might call an adult a child if you thought their behaviour was immature. You're not saying that there's anything wrong with being a child, just that an adult behaving like a child is worthy of criticism. Obviously the other words are a lot more emotive than "child" and I'd never refer to someone with a disability with any of those terms because that would be to suggest that there's something intrinsically wrong with who they are, which I don't believe there is.
Also, I don't think that there's any comparison between insults like these and racial slurs for example, because race is irrelevant when it comes to intelligence, etc. So, to even believe that drawing attention to someone's race is an insult to them, requires you to be a pretty had-core racist in the first place.
