Wall street has the smartest people on earth working at those companies.  I know it's hard to believe given how stupid they have behaved at times.. but they hire the absolute top from places like MIT and Harvard.

It's hard to think that we could even imagine the schemes they might cook up (good or bad schemes I guess).

But overall speaking I'm betting it's a good thing ($/BTC -wise) the more wall street gets involved.
And like another said above, it's necessary for BTC to advance for it to get widespread and common-place investment options.
Let's face it - not that many average Joes are going to be interested in holding a chunk of their investment in some online thing called a wallet or some 'paper money' thing that they have to encrypt and store offline for max security..
They'll prefer someone else to worry about all that and just offer them an insured investment option (i.e. if you buy the Bitcoin fund from the Winkelvosses and they get hacked for a few BTC, their investors can feel secure... they can sue them if they want even, etc. etc. etc.  May not totally safe but they'll feel safer doing it that way).