General rules:
Exceptions may be made at the discretion of the mods.
This is on par with the Joker for “reasons the rule against heroes killing is stupid.”
Seriously, if a guy who has already committed murder provides a roadmap for how he plans to do it again and is perfectly capable of executing the plan, what more do you need?
The problem with the Reverse Flash is that his time-travel shenanigans mean that you never really know when you're dealing with him. Is this him on his first outing? Or is he already done killing everyone you know, but you managed to defeat him and fix everything and now he's showing up for round two or fifty? He's traveled across timelines so much that he's effectively immortal. He's been killed, but still shows up because the one that Barry killed was him on a different jaunt in time. There's absolutely nothing linear about the Reverse Flash.
Remember that time you trusted a fart that you shouldn't have while doing a presentation in front of the class? IT WAS ME BARRY! I WAS THE SHART IN YOUR PANTS!
Comics are just like soap operas - when you run for so long you have to try every permutation of every story. Including "time travel to kill mom, pose as social worker and raise barry as his own son". Probably twice.
And still those levels of unreasonable and borderline stupid hate is a much better villain character and motivation than almost anything we get in media these days. Including the second half of reverse flash's arc in the flash tv show!!!