and yet they're generally considered valiant heroes.
By whom?
By everyone throughout history who has enjoyed stories of valiant heroes. Were you really asking a question here?
I think Eugine Nier was talking about real-world warriors, not stories. (I don't think all the people who enjoy watching HIMYM for the Barney Stinson character also have positive attitudes towards real-world PUAs, I know at least one person (namely myself) who enjoyed playing Carmageddon but is generally horrified by real-world serious violence for frivolous purposes, etc.)
IME people who worship warriors as heroes tend to come from the right-wing/theist/low-Openness/nationalist cluster, and there are plenty of people from the other ‘side’ who condemn them ...
Rationality quotes time!
The usual rules: