Their clients would sue them and win.
If you're worried about that, then don't invest in XRP. You only need tiny amounts to be able to use the Ripple functionality for other currencies, including BTC. And of course, OpenCoin has no motive to do this, because they would be shooting themselves in the foot if they did. They want the XRP exchange rate to go up, not down, just not uncontrollably.
The protocol is distributed, just like Bitcoin, so governments cannot really shut it down any more than they can shutdown Bitcoin or Bittorrent.
5) What if Ripple itself gets hacked (source is still closed so no one knows how secure it is, there may be major security flaws)
6) What if Opencoin decides to randomly start doing bad shit like making more XRP, confiscating balances, banning accounts...etc..
Only a problem until OpenCoin releases the source code. It is in their interest to do so, precisely because it will dispel fears like that.
Basically Ripple makes Opencoin the de facto Fed...
Scare mongering.