First, it's escapist fiction, so it's supposed to by over-the-top. I enjoy the characters in NCIS-LA, but in almost every episode there is a scene where they blow away everyone who might be a bad guy.
No one ever investigates afterward. Nobody gets put on administrative leave until it's determined the shooting was "righteous."
No foreign government demands the U.S. answer for agents who shot up a whole neighborhood. If they even make a peep, someone, usually Henrietta, "handles" it. The question of whether all those deaths were warranted is ignored.
The assumption is the good guys are the good guys, so they get to kill bad guys. Period.
The opposing arguments hold that indiscriminate killing sends the wrong message, in fact, a whole bunch of wrong messages.
Shoot first and ask questions later.
Anyone around a bad guy must be a bad guy, too.
Death is the only/best punishment for those who hang around with bad guys.
It happens in books, too. Yesterday I finished Lee Child's newest, MAKE ME, and there's a lot of "kill 'em all and let God sort it out" mentality. Child makes his bad guys pretty bad, so the argument can be made that killing them is justified. We tend to like vigilantes when their practices "save the time and expense of a trial." So much for that Constitutional stuff about innocent until proven guilty.
I don't really have a side in this argument, as long as we're talking fiction, but the unfairness of it does flit through my head when I see/read such things. I'm more comfortable in STAR WARS, where the legions of soldiers shot, bludgeoned, and otherwise put out of commission are robots, not people with mothers, brothers, and even sons and daughters to mourn them.
Bang, bang, shoot-em-up is okay for entertainment, as long as we recognize that in real life, those things support the "eye for an eye" mentality that keeps violence going. Maybe some people need killing, but that's not a task to be taken on lightly, even if you've got a badge, a mission, or what you consider a good reason.