are they trying to cut prices or speculation?
Both.
By selling naked shorts, the Evil Empire drives down prices. This triggers stop losses and margin calls which further increases sales and drives small time traders out of the market (further cutting prices in both cases). Then, at some future price, the EE buys back the shorts and books a nifty profit.
This works great providing the market cooperates. Unfortunately for the banks, the silver market shot up so far so fast that they were unable to unwind their position without causing further damage (some estimate that JP Morgan Chase alone is down about $5 billion at present). This is why the bank's are so desperate and their trading fraud is so blatant at the present time.
Many predict the scheme will fall apart before the end of the year. Silver prices will increase substantially when this happens. Your guess is as good as any as to how high they will climb.