Free market is best.
However my question was different: As 90% rule is in place why there is no 110% rule.
First it helps to get terms defined in a way that is clear because 90% or 110% depends upon which way you view the order book.
The "actual rule" is "though shalt not short new BitUSD into existence at prices that would devalue BitUSD relative to USD".
You can short at prices that "over value BitUSD", but in this case you are likely to be out bid by people willing to sell their BitUSD closer to the Peg.
The other way to view the rule is this: shorting is only provided when demand for BitUSD exceeds the supply of BitUSD at the peg price.
So the market is fluid and unrestricted between BitUSD and BTSX longs, it is only restricted in the new issuance.
I also think that in the scenario where I am hit by a bus, BTSX should not be so volatile that BitUSD will become worthless. There are many developers who can work on the system and it is already mostly there.