Psyringe: Well, most mods already _are_ in one or two places, and these places have rating systems, discussions, large communities, etc. In which way is adding a _third_ place to the mix achieving the alleged "get all mods in one place" goal?
It's basically to get all those on board, who didn't modded before. Just a quick look through steamforums gives you a glance of the "issues" the Joe Averages had or ran into once they tried modding.
Yes, most of those probably fit in the "dumb as a brick" or "barely manages to click install" category. However, you won't get those to experience this new world the old way. Probably not even with the Nexus Mod Manager.
Psyringe: This service simply isn't needed imho. It has proven to be an additional source of problems and errors for Civ5. I think there was also some contention because some mods weren't allowed on Steam. In any case, I don't need Steam controlling my _mods_ as well, and I would be very reluctant to grant a new quasi-monopoly of control over mods, to exactly the same guys who are already abusing their existing quasi-monopoly on new games.
Not needed - for guys like you and me who modded Bethesda games before: you're right. For all else: you're wrong.
Additional source of problems - can't say I'm experienced enough to judge Steamworks at all. Though it's easy to see that this is THE big chance for Valve to promote / make use of it. So I'd bet they'll run to hell and back to make it as painless as possible.
Some mods weren't allowed - yeah, will certainly happen. However, there are rules / removals on TESnexus too.
Control - as long as mods are also available like before (nexus / PES), which I see no indication of not being or happening so, I don't see the problem.