PG thinks the death penalty is bad, but PG isn't worried enough about other things you think are worse, therefore PG is wrong? (???)
I honestly don't see where you're going with this other than cheap sniping.
He's anti-death penalty in the same way. The orders of magnitude more suffering in our prison system can't get a tweet but the nearly disused California death penalty urgently bothers him...
It does seem to bother Paul Graham as he writes "The police often arrest the wrong person. Defendants' lawyers are often incompetent."
It's also clearly an argument intended for Other People who need pragmatic reasons for ending the death penalty. He is against it on purely ethical grounds, or in my opinion, because it makes him feel bad about himself.
The agenda is:
1. End the death penalty.
2. Assume someone else will help innocent people, which they largely won't.
3. Go bad to enjoying blissful ignorance.