GLD doesn't have a large amount of short positions. According to
indexuniverse the short interest was -4.8% of the shares outstanding in Feb 2011. It could be larger, if more ETF investors wanted to short it, but it isn't because they haven't. (Compare Spider's S&P Retail Select ETF, Ticker XRT, for an example where the net asset value is a very small fraction of the total longs and shorts)
Nonetheless, it is the case that any ETF that allows shorting (which is not naked shorting since the stock has to be borrowed first and collateral has to be posted) can have long positions and short positions that are greater than the underlying assets in the trust. (The same is true for individual stocks and bonds.)
To repeat, nobody who is opposed to fractional reserve banking or central bank management of the money supply should trade ETFs, because their position would be internally inconsistent with their ideology.
They should also be petrified of serial runs on ETFs destroying their market value, as
Andrew Bogan was in the article that produced a swathe of rebuttals last year (Another rebuttal
here)