Would say Kenny killing Carver was right?
Ordinarily, I'd say no. However, with how dangerous Carver was, and that if left alive he would just come after the group again, he was to dangerous to be kept alive. So, it's not like there was a lot of choice in the choice in the matter.
Here's a couple of ways I see it.
Whether or not Kenny made the wrong choice. I think Kenny did what had to be done. Carver needed to die.
If I was playing as Lee,( if he had survived season 2 and all), I would've killed Carvers myself. Although not like Kenny did. Rather I would shoot him in the head and be done with it. That way, Carver doesn't suffer, and all the ones that Carvers killed are avenged. Not to mention the fact it's more humane.
The other way I look at it is....
After Carver murdered Walt, I think Kenny, from that standpoint, was justified in killing Carver. There was no need for Carver to do that. And afterward, Carver had that murder, and later on Reggie's murder, plus possibly dozens of others to account for. "Eye for eye, and tooth for tooth!"
So after everything is said and done, I think Kenny was right. However I did not enjoy seeing Kenny killing him so brutally. A simple gunshot to the head would've sufficed.