Go with the pink. Decency will bring in more members than those who get expelled. What makes you think people won't go pink in a cdz politics forum.
If the pink option is chosen, probably more than half the USMB membership will get gone. If I am wrong, please correct me. Forums need traffic, so nuking more than 30% of your membership quickly goes against that. Personally I would subtly and gradually change the forum, making the atmosphere increasingly inhospitable for trolls, partisan hacks, and the like. Take out some of the more vocal trolls and hacks first, increasing the rate ever so slightly over time, and with every nudge people will adapt to the change.
Maybe.
Sometimes it takes healing a problem slowly, than taking a drastic action early on. People who go to the CDZ and break the rules—knowingly or not—are undoubtedly dealt with by staff.