The idea of 'supporting the value of steem dollars' against market forces is a bit like asking people to pay more taxes than they ought, just to support the good ol usa, be patriotic. If the 'value' of the steem dollar is less than the dollar, then it is so.

What we are talking about with SBD is a little different though. The idea behind SBS is for it to be worth approximately $1 USD worth of Steem. The proposal is to basically tweak the numbers/formula that is used to calculate how much Steem one SBD is worth, to make it closer to $1 USD.