Buffy is a human endowed with demon-based powers. That doesn't make her a demon. You're reading into something, which is perfectly fine, but that doesn't make it fact or canon.
This is a murky area. I dont think you can say that Buffy is 100% human, but with extra abilities, a vampire is a human infected with a demon and no soul, Angel and Spike are humans infected with a demon with souls, Buffy is a human infected with the spirit of a pure demon, I can't see how much different that is from Angel or Spike, she is a human/demon hybrid.
The only thing that really says otherwise is that Spike can hit her, but we dont know the specifications of the chip, it could be the presence of a soul that would have stopped him from hitting her, it could be that she looks human, there's a lot of factors that to that.
Spike could hit her once she came back from the dead, that might have mean she was 49% demon before and 50% when she came back, those few molecules of difference mean she was on the verge of not being recognized as human by the chip.
Vengeance demons dont seem to be anything more then human, except with extra abilities, same as Buffy.
Wrong.
I just proved to you that prison is a viable alternative. Warren was a human killing another human with a gun. That is EXACTLY what the prison system is there for.
Killing Tara wasn't Warrens only crime, it was his
latest crime. He was a small petty little person who didn't like being shown up by women, he never would have let that go, even if left Sunnydale he would have continued down that path.
Even in jail, I'm sure he would have been working on something to get out of there and the means by which he would have been doing that wouldn't have been something normal police could have stopped.
We can't even be sure they could put this on Warren, it was in Buffys home, no cameras. I'm sure Warren could have gotten rid of the gun though means the cops couldn't investigate.
After he though he shot Buffy he went around bragging about it, he didn't feel the need to lay low even though police would be involved if Buffy had died from a shooting. The only reason Warren fled was cuz he thought Buffy would be after him, to think he wouldn't have something in place to deal with regular police is crazy.
When he find out Willow is coming after him, he has no problems in killing her by trying to stick an axe in her back, the dudes a loser who was shown to have little to no humanity unless it was about himself, no reason for him not to die when other humans like Ben and the knights were allowed to be killed for the greater good.
I would refer you to your own quote of "this thread is about Warren only", but I can tear this one apart too.
Ben had to die because he was embodied with Glory, and there was no way to prevent her from surfacing again. Warren had no such affliction. There aren't even remotely comparable.
Wrong.
Warren didn't die that day in the forest and he did come back and terrorize Buffy and Willow. Warren was the exact same situation as Glory, no matter how long it took he would come back, he wouldn't let that go, being humiliated and defeated by a woman.
That is fact, he did it, that is what his character is.