That wasn’t an intention title pun.
I was browsing some things I noticed that his comics seem to share this frighteningly nihilistic vision of brutality and violence, where everyone and everything engages in horrific actions, often just because. It honestly seems like he has a series hate-on for, well, everything, but particularly religion. Or at least God, for some reason. And men. And women.
Does he have some issues or is it just me? Heck, the Preacher series alone could fuel a lot of psychotherapy bullpen sessions.
Ennis and his peers seem to have missed the point that absolute evil is no more realistic than absolute good. Things like Preacher or The Boys are just the flip side of Archie or Richie Rich. I prefer my comics to have a little nuance.
I think he just dislikes superhero comics and set out to piss on them wherever he could.
The best Ennis heroes are military or ex-military types (Fury, Punisher, Tommy Monaghan, Phantom Eagle, Dan Dare, Battler Briton) held back by less-qualified superiors who are political hacks. I don’t know enough about his personal life to make any connections.
Frank Miller has issues too, but that’s another thread 
Except his issues come through loud and clear even when he’s not writing Superhero comics.
The only difference between Preacher and The Boys, Ennis’s-Issues-wise is that Preacher has the undercurrent of Religion Sucks and The Boys has Superheroes Suck.