Really depends on which game, and yes the forums are moderated by Steam staff, who at least understand the role correctly (internet janitor, not little personal fiefdom)

To pick a random game's forum: https://steamcommunity.com/app/1623940/discussions/ we find:

- bug reports, feedback to the devs, etc.

- asking for help in the game

- story discussion

- requests for games like this one

- concern troll (locked)

- begging for the game to be released on GOG

Seems above board to me. I've also seen plenty of trolling, incivility and unreasonable expectations from manchildren, but they tend to get locked.