First, Killing yourself would not be doing humanity any favors, the callous b@st@rds wouldn't even notice.
Second, because they are callous and unfeeling, you owe it to yourself to vindictively burden them with your presence for as long as physically possible.
I'm joking, of course, but if trolls are harassing you, the best advice is Don't Go Where the Trolls Are. Hard to do, I know, since the Internet seems to spontaneously spawn them by the millions, like Sea Monkeys, but their nasty remarks can only hurt you if you read them, so don't read them.
I rarely go back and read replies to my own posts here on WP and these people are generally pretty nice. My state of anxiety is just naturally so high, it doesn't take much to twist me up and make me feel like I'm being intentionally brutalized, and I know a lot of that is my own perception, but it doesn't change the fact that that's how I react, so I just preempt the stress by not looking back.
Also, writing is like any other art form. There's Definitively Great and Abysmally Awful - and a giant ocean of entirely subjective opinion in between. One person's favorite literary treasure is another person's toilet paper.
Even if you start out closer to the Atolls of Abysmal Badness than to the Harbor of Definitive Greatness, you can learn to swim and strike out for clearer waters. That is, after all, how you get to Carnegie Hall.
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"I don't mean to sound bitter, cynical or cruel - but I am, so that's how it comes out." - Bill Hicks