Seriously. Seriously. That wasn't psychotic, sociopathic, or insane. Immoral, sketchy, ethically questionable, yes.
Randomly, and separate from Livia's post.
What seems to be overlooked is that Wallace is the least innocent victim here. He kidnapped Jeannie and then McKay. He injected Jeannie with nanites to get them to work on the cure. He did not fall from a magical cloud of innocence to be brutally killed so John could continue getting free access to Rodney's ass and/or satisfy random bloody urges. Wallace injected Jeannie knowing there was no cure. If Jeannie had died, he was a de facto murderer right there--it was premeditated, he did mean harm. And I'm pretty sure that "I didn't mean to kill her with it</i>" isn't going to fly in the face of the fact that at the time there was no cure for the nanite problem.
It was ethically wrong, and probably bad bad bad--but on the other hand. Hmm. On the other hand, I don't see a problem with it at all. I don't have a problem with John killing Kolya when Kolya was going to kill him and his team, or the Genii in The Storm/The Eye who were going to kill teh people of Atlantis, I had very little problem with Ronon killing his commanding officer for fucking them over, I seriously have no issues with the death of random Wraithes at all.
I'm not sure why Wallace gets a special classification when he's as guilty as they are.
And I dont' see how a choice that John makes between the life of Jeannie (and Rodney, the Pegasus galaxy, and maybe all species of life in the universe) and Wallace falls under psychotic.
To me? It feels pretty damn human.