The basic difference between SPS drawing from inflation (rewards pool) directly and using their earned rewards to do so is that the former is a tax over which individuals have zero say over how much they pay for what, and
has complete and total control over how they spend their personal funds.
Taxation is theft. Goons always take charge of any taxation, because thieves steal. If voluntary contributions aren't forthcoming for development, there's a good reason for that.
RE: HF21 and the Steem Vision