Yes, using "male" or "female" as a noun (rather than an adjective) is bad form when referring to people. At least, it's non-standard.

That said, language is constantly evolving, and when there is a need, it will be filled. Convention be damned. And there is a need for a noun that means "girl or woman" that isn't clunky. There's no good "standard" word to use. I think that's one of the reasons this usage is becoming more common. (Personally, it gives me the ick, probably because I heard it used mostly in misogynistic contexts c. 2010 and it's hard to shed that connotation. But I see it more and more without that subtext more recently. I suspect in 50 years it will be "standard".)

Similar deal with the singular "they". Some people still complain about that, even though it's been in use for a very long time (centuries, I think).

I, for one, am a strong proponent of...well, my username. After all, "bro" can be short for Broseph or Brosephina.