Trunks gets such a look with that, something between annoyed and flat, towards that little title of Goku's. You really didn't have to go that far, Trunks.

Fine, let him educate you, boy. "There is a number of times Kakarot should had and could had ended a fight, but chose not to. Either because he wanted to give them a chance, or it wasn't enough of a challenge for him at the time. And every time he did it resulted in our opponent being able to pull off some bull shit they wouldn't had been able to if he had the guts to just end them when he should had." Vegeta is all for a good fight, has a need for it, but he also recognizes when he has someone beaten and to get rid of them. And when they could be a greater threat later if not dealt with at the time.

It wasn't mindless slaughter like he once used to do, it's getting rid of a danger that could come back for them later.