I don't care if he wrote the fucking Bible - he's a mass murderer and the world was better with him in Supermax.
I wouldn't exactly call him a "mass murderer", he only actually killed 3 people over a 17 year time span. IMO a "mass murderer" kills a lot of people all at once in a single location, for example, like McVeigh.
Relatedly: What's the threshold for you for body count before someone loses credibility? 5? 10? 100? 1000?
I don't think any of those necessarily makes someone lose credibility for their writings.