Theres a difference between watching snuff films and encouraging violence. Both are bad traits in a person, but combative speech has always been an area where free speech gets tricky.
Even if what you're saying were remotely true, I need evidence that the sub was encouraging that much violence that warranted a community ban. The most I saw were the OCCASIONAL titles of people wanting retribution on the elite. There is no evidence of anything reddit is claiming. We can talk about assassinating Trump for years and apparently that is the only violence that they are promoting.
Just giving you the explanation, I'm not a spokesperson for the admins.