But its not KKR listet on the pro SOPA list its one, and only one of there portefolie companies. KKR are not (in the same way as YC isent) responsible for its portefolies standpoints.
They are not legally liable, which is different from being responsible. Imagine if one of their portfolio companies was a child porn distributor. You wouldn't defend KKR, because clearly they have some choice in who they put in their portfolio, and a child porn distributor is an immoral choice. Holding a SOPA supporting company is also a (albeit less egregious) poor choice. Taking away invites of their portfolio companies provides motivation for them to look into this sort of thing when choosing companies in the future.
They're an enabler. You punish them the same to inspire them to push pressure downward on everyone they work with.
Remember when Glenn Beck was still on Fox and people were crying continuously? Nothing worked until they started boycotting the companies advertising for him.