Of course Sam would save Dean if it was within his power. BUT Sam said "The same circumstances" meaning he wouldn't take Dean's choice away/trick him, like what Dean did to Sam. Sam's been tricked/manipulated by Lucifer, angel's, Ruby, being fed demon blood etc and he's upset cause Dean lied to him and won't say sorry.
I'm sure he would have done the same thing. Maybe try to find some other way keep Dean alive, and for this time to come up with other methods are exactly save him. When Sam said this, it spoke of anger and resentment for him. And this doesn't mean that he wouldn't save his brother at all. Just in the same circumstances... he would try to come up with something else, or would just talked openly asking Dean accept an angel.
Sam just angry at his brother, it would be hard to accept that his hands have killed Kevin, but he would save Dean, I'm sure. Carver just bad knows this character if he think Sam didin't save his brother. He shoul re-watch 1-5 seasons.