Even if their body counts are minuscule in comparison; heroes who kill for vengeance will always be shed in a bad light in comparison because there has to be a line drawn somewhere.
Of course, it’s more than fair to say that intent plays a role.
It’s certainly a worse look when Deadpool killed a surrendering victim or when John Walker killed a defenseless terrorist compared to when Iron Man nuked an entire invading Chitauri army.
Otherwise, we’d all kind of have to admit that heroes largely act as judge, jury, and executioner most of the time, with small exceptions made in the case of the vilest of villains.