A bill to cut off all funding to ACORN is unconstitutional. A bill to deny funding to any contractor who works with the DOD who denies the right of rape victims to sue in court for their injuries is constitutional. These are different situations.
The difference is key - one (cutting off funding) is designed to make illegal actions that affect ONE entity - ACORN. This is called a bill of attainder and is expressly prohibited in the Constitution. The other (allowing rapists to sue their rapers) effects ALL entities that would contract with the government and is perfectly legitimate. It doesn't make actions that happened before the bill illegal - that is to say Jamie Leigh Jones still won't be able to sue Halliburton or her rapists (alleged) over her ordeal. That would be unconstitutional as an ex-post facto law. But going forward, unless Inouye gets his way, then future injuries of this kind would be viewed in court. It doesn't require that defense contractors quit putting rape arbitration clauses in their contracts. Rather it says that defense contractors who don't take these clauses out will not be able to contract with the government. (He who pays the piper calls the tune).
I've been having troble with embedding video recently on here, so I'm going to direct you to Glenn Greenwald's site, where you can watch a video of a congressman being educated on what you would hope he would already know (though he's a Republican congressman, so perhaps ignorance of the Constitution is allowed?)