I don't think any of your argumentative points were the least bit invalid - I agree completely. But you do have a rather confrontational tone at times; saying "Prove to me that having a uterus has a direct positive effect on intelligence and I'll consider withdrawing this point" (and quite a bit of what follows) could reasonably be taken as offensive. It seems this person was more irritated by your tone than any point you were trying to make.

Just my 2c.

I think you're dealing with somebody who doesn't like you, personally. This "Brihana", whoever s/he is, seems to think you have a track record of hating women, or trolling, or something. Who knows?

Your being annoyed at that fic is a legit complaint. Why in the world would a sex change affect your mental functioning? I guess maybe you could get side effects from the hormone treatments before your body could get used to them, but that's drug side effects, not a gender thing.

Re. male and female intelligence: You are right in that the average values are the same. However, males and females have very slightly different specialties (on the order of a percentage point or less)--which means very little for any particular man or woman, because the difference between genders totally vanishes compared to the difference between individuals.

Also, males tend to have a slightly larger standard deviation in their distribution--that is, they have more scores at the high and low extremes of the range. I think that's because men (usually) have XY chromosomes, which means that anything on their single X will express fully because there's not another X to provide another gene that can partly/fully cancel it. As a result, we end up with slightly more gifted and more cognitively disabled males than females--though not by much. But anyone who's XY will get that effect, whether they're male or female.

I betcha the person who's harassing you knows you write for the PPC. That's what happened to me a while ago on ffr, when I used my PPC LJ account to complain about OOC characters in bad slash and everybody apparently figured that made me a homophobe... somehow.