The problem with currency, especially when it comes to cryptocurrencies, is that too many factors go into maintaining its value to perfectly stablize it. Even with an arbitrary peg, innovation will eventually render it useless. For example, salt was once a prized currency, thus the idom "worth his salt".
And to make matters worse, is that the attractiveness of these currencies is the lack of regulatory agencies and governments to oversee and control them, which make them even more volatile. Of course you're right that asking people to support the value is ridiculous. It's the responsibility of Steemit to make sure people use their currency and that interest and confidence in it stays high. The current system is meant to do that but not as many of the major players or "whales" as they're called, are reinvesting the value back into the platform.
yes, it is impossible to prop up a currency, at least not for long; there is much talk about the dollar faltering, and even possibly crashing, as it has been propped up for a long time and so is in a bit of a bubble.
. the best thing they at steem could do is to enable easy conversion of their currency to others, such as bitcoin, for little or no cost, and the reverse, conversion of other currencies to steem 'dollars'
. changing the name of the currency from 'dollar' to something else would also be good