That's easy - Reddit would simply remove the mods who were refusing to moderate. That's long been against reddit's terms and conditions.
Of course that just brings the conversation right back to how Reddit thinks its subs will cope run by brand new inexperienced moderators.
It depends what you want out of your system. If you just want a "plug and play" machine that will do most things reasonably well, by all means stick with Ubuntu.
If you want complete knowledge of exactly what you've got installed (and just as importantly what's not been installed) and how it's been set up, and tuned and tweaked to your ideal requirements, Arch is a great choice.