It is not normal or okay to receive death threats after presenting at a professional conference. I've presented several times and have never received a threat. I can't even imagine that happening.

Maybe there are some subcultures where this behavior is something "Everyone" experiences. Certainly that's not the case in mainstream tech.

(As an aside, techies aren't the only people who use the internet, and I'm pretty damn sure that receiving death threats via email after presenting at professional conferences isn't a thing.)