@feha Yea, as they say, all is fair in love and war...which in another way means, nothing is fair.
There is no pretty side to war. No good or evil. It's just humans fighting against humans for their greed, their own benefit. Anything that's not with them is against them basically.
Justified or not, he was in a kill or be killed position. Just because he planned through and is overwhelming them doesn't make him the bad guy. If only he was barely hanging on and desperately surviving here people would've had a completely different reaction in the comment section.
If you look at the big picture, he's not really doing anything bad.
A den of blackmarket criminals got outed and the elves who were all supposed to die, one to be turned into a slave, and the other to live the rest of her life in guilt...well, they're all dead now. Initially it was the fault of the elf queen, but now it's the fault of the MC. Result is not much different, he knows what was supposed to happen originally so what's the problem of changing the cause a bit if it benefits him? He IS the hero you know? His gaining of strength is their salvation basically.
So even if he was a good person, I still wouldn't feel very bad for him doing this. So far his actions are still quite mild. If people are already having trouble with this, they definitely shouldn't read any further.