It doesn't need to be a lot, but I highly, HIGHLY agree that d3 should be pay to play.
Even a few bucks a month will allow blizzard to fight bots a lot more effectively.
Just look at what Diablo 2 has become. bots plainly rule the whole of battle.net
Chat spam bots, game spam bots, farm bots, baalrun/diablo run bots.. the list goes on.
Looking at WoW, there are still spambots there. But compared to Diablo 2,, oh man... there's a HUGE difference.