It greatly depends on who/what the team is fighting against and just how lethal you're asking them to be. Of course there are heroes that kill, but many of them are able to take down super villains without killing them and may feel disgusted being in a position where they already defeated the threat but then they get killed anyway. If it's like a specific cover strike force then you'd get heroes that are more "spy" like in regards that they'd prefer not operating on a super public scale (Black Widow/Wolverine/Agent Venom/Deadpool/etc.) while being on this team. However if you're putting together a team with a more Punisher like mindset where "we need to punish any supervillain that's a major threat regardless the outcome because they're too dangerous" then you'd have a smaller list. Honestly it's a little harder with DC because many heroes there sway more towards not killing or don't do it unless under extreme circumstances while in Marvel threat are heroes that kill or have an easier time but even they put thought into their actions and may prefer sparing someone just because they aren't at nature bloodthirsty.