After what they had Oliver just admit, I am interested in where they are going with it. I thought he was just going to admit he was a murderer and not a hero (i.e. referring to times he killed when there were better options, and that making him similar to a lot of his enemies). I did not expect him to say he "liked" it.
That's the thing, though Oliver in the flashbacks and in S1
was a monster. He's not now. Even if he liked it, I'm sure he has consciously suppressed those feelings ever since Tommy died. But what would bring back something like that? Tragedy. Remember every time he's ever killed/threatened to kill someone: when they hurt someone he loves. He killed Vertigo for threatening Felicity. He threatened to kill Slade after he killed Moira (didn't follow through). He killed some Ghosts after Felicity was crippled. He killed Darhk for killing Laurel. And he started killing again for a brief time after Laurel died. The only kill he's made that was based more on necessity than on revenge was Ra's.
So I don't think Oliver enjoys killing anymore, per se, except maybe the deepest, darkest recesses of his mind, but he's fully aware that he used to. Look at the flashbacks: after he killed Fyers, that's when it really started. He pounded that guy's brains in early in S2. He killed Ivo. He killed Slade. He killed a drug dealer for selling to his sister. He tortured Shrieve
brutally for killing Akio. He killed Taiana's brother in self-defense but he killed Conklin (as much for his own personal hatred of the man, I think, as for the other prisoners' sake), he killed Baron Reiter, he killed Taiana. At this point, all he even knows is killing. Then we get to S5 when he's trained by the Bratva to be even more of a selfish killing machine, and then by Talia to channel that bloodlust into "justice."
Looking at all that, honestly, it's not strange that Oliver enjoys killing. Rather, it's a miracle that
he was able to stop. That, I think, is what turned Oliver from a vigilante to a hero. He saw the monster he was (through Tommy's eyes) and changed. And sometimes that monster slips through, but with the help of his friends, usually Diggle and Felicity, Oliver has come a long way in turning that around.