If they don't, it really doesn't matter.
Exactly. I can't at all understand any anger from this announcement.
The absolute worst possible outcome is that Valve doesn't filter shit well, most of the offerings are overpriced, and so no one uses it. Then it'll disappear and people will make and download mods as they have in the past.
Folks seem to conflate their feelings about "I don't think this will be an effective pursuit", with "OMG! How could they ruin everything like this! AHHHH!". Just because something might be implemented poorly doesn't make it also some kind of war crime.
I think Steam trading cards have proven that selling useless and overpriced shit can be a very effective pursuit.