I don't understand why he or anyone for that matter would care what other people think if they can't articulate it in a civilized manner. Nasty emails is what the delete button was made for.
Its a cumulative effect, the individual e-mails can be laughed off, but you are spending the energy to hit delete. Its e-mail without a spam filter of any sort. Its not the first e-mail that will get you, its the thousandth. No one survives being told they suck thousands of times unless they build a hell of a attitude and we get projects that are "mean to newbies". A lot of legitimate newbe questions are indistinguishable from the opening volley of a troll.
I can totally understand why someone would still be emotionally drained from receiving lots of criticism, whether they intellectually know it's silly or not. It's hard to have the self-confidence and restraint to maintain a good attitude when you're surrounded by criticism.
We're social animals and we care what others think, at the DNA level. We're also evolved, and we can recognize what should be paid attention and what should not. But we can't entirely escape our DNA, and we vary from individual to individual on how far we can each escape. We're not code, we're wolves.
You can dismiss the infrequent and brief squealing in your ears, but once it becomes tinnitus, the incessant, constant high pitched tone makes it impossible to focus on anything.