The reason that facebook has such a substantial market capitalization is because of its earning capability. I have not heard a single revenue stream for steem presented, so comparing steem to facebook in the way that you have doesn't make any sense. You can't really base the success of a company on the speculative interest of a crypto currency - it certainly didn't work for bitshares. If the platform doesn't have revenue, don't expect for there to be investors to bolster the market cap upon which the payout scheme depends.

Additionally, I think it interesting that you talk so frequently about the subjectivity of value and make a claim such as "a blockchain currency is inherently more valuable than a centralized currency." A centralized currency with more widespread use than a blockchain based currency is indeed more valuable to the general public. If the use of steem and steem dollars is confined to users of steemit why then does steem have to be a blockchain based currency. Venmo works perfectly fine with crypto currencies.