I've seen extremely negative comments left on stories that I adored, by writers I considered to be among the best in any fandom, ever. Since then I've always told myself that you shouldn't take harsh criticism too seriously. Sometimes people just go around thinking of nasty things to say about every story that features a certain pairing they don't like, or something silly like that.

I'm sorry to hear you had such bad luck with your first story years ago -- and pure bad luck is what it surely was, to have attracted the attention of an idiot on your very first story. I was "lucky" enough to have that happen to me only after I'd already posted quite a few stories in various fandoms, so it was easier to shake off.

I hope you can convince yourself that such a critical email certainly was just bad luck, and no need to see it as a reflection on your writing!