The mission always comes first. Sometimes necessity dictates there is no alternative. I'm not defending Hollywood. I am simply pointing out there are plenty of reasons why there might be no choice and it has to happen.
I'm pretty sure no one on Omaha Beach was thrilled with the battlefield. They did what had to be done.
In reality, it's very very occasionally justified. In Hollywood, it happens in almost any "war movie" one watches.
If it happened in movies as often (or as rarely, rather) as it happens in actuality, and it made sense in the context of the events, then it wouldn't piss me off. Instead, it happens routinely, and without justification.
"But it could happen once" is not justification for depicting something that way EVERY **** TIME.