This might be the goal.
YC has been fairly heavily criticized for comments on certain topics which don't toe the party line. Mitigating such comments may be beneficial for YC (the business) in order to avoid negative publicity and attacks from powerful adversaries looking to score a symbolic victory [1]. Remember "The [mis]Information" interview with PG?
Discussions of such topics are mostly a distraction from what most of us come here for anyway, so it likely would not hurt HN much, particularly if it is turned on in sensitive threads only. In my view banning such topics would be a better solution, but I'm aware that HN has been attacked by critics for the soft ban (which pushes such stories down quickly), so this might be the best compromise for the business.
(It's important to remember that YC is a business and HN is just advertising for the business.)
[1] YC is a good target for such a symbolic victory since they are weak supporters of the cause and are unlikely to fight back too strongly but are also highly visible.