Seriously, that's a completely **** comparison of behavior, reflecting absolutely none of what makes this discussion tick. You're better than that.
Why, exactly? If his hypothesis is that repeatedly insulting someone, or groups of someones, will lead to that group of people eventually becoming desensitized to being insulted, I want to see some proof. Personally, I believe that this is very much not the case; especially when talking about groups that receive a constant influx of new members. Someone is bound to take offence all over again, thus restarting the argument.
In addition, labelling a certain group of insults to be basically OK to use because "they need to grow up" is a rather silly concept in my opinion, and certainly does not deserve to be taken even remotely serious.