Large financials could use their financial largesse to buy up large quantities of the supply of bitcoin in order to undermine it by creating volatility, manipulate its price or reduce bitcoin liquidity. Bitcoins divisibility helps to offset the liquidity aspect for quite a while I suppose.
What do others think? Could this potential threat be combated as bitcoin becomes more of a competitor to the major established financial entities?
By the time bitcoin become big enough to be viewed as a serious competitor, it would be too late to buy up large quantities of bitcoin.
IMHO, large financials would use other methods, namely their political clout to make BTC illegal. It may harm BTC, but it won't kill it, just slows it down a bit.