Ah, I do agree with most of what you are saying. You do make a good point. It does offend others who are not targeted by the insult, and that's not nice. Then again, neither is name calling. Doubly not nice.

But I think there is a small problem. It's not that insults draw from something that is always bad. It's more that insults draw from something that offends or causes an emotional disturbance. Calling someone X doesn't mean that X is bad, it just means that the name caller believes that being called an X will be upsetting. Often times, these two things overlap, but not always. The ultimate goal is always to make the other person feel negative emotions, not to make a statement about others. But I do agree that insults often have collateral damage.

I think that the practice of calling someone gay as an insult will fade once the backlash of using that insult outweighs the benefit (ie, the amount of emotional trauma caused to the victim).

I also agree that generally, being dumb is a negative trait, but I also believe that it is mean to people who are just born with slow brains. Nobody gets to choose the brain chemistry they are born with, and it's not nice to say that all dumb people are bad, or imply that dumb people are bad people by calling someone bad, dumb. But the amount of backlash you'll receive from calling someone dumb is incredibly minimal, and I don't see that changing any time soon, so the insult will likely stay. As for homosexuality, we are lucky to be living in a time where acceptance is rapidly spreading. So hopefully, there will be a cool new hip insult we can call each other on the internet without offending people that like to bone their own gender.