I strongly disagree with a lot of your argument, but the level of downvoting here is still interesting. I suspect that this is happening for three reasons: 1) The belief in question is as you correctly note associated with some people who still exist and are pretty low status. 2) Unlike something like infanticide or slavery, there's a perceived chance that this sort of thing might actually go back to being this way (see the existence of people mentioned in 1) and thus this feels to people like it is much closer to an actual political mindkilling issue. (Robin Hanson might say that infanticide is far but patriarchy is near.) 3) There's been some problems in the past with a perception that there's a cadre on LW of people who have essentially implied that women are of less moral worth than men (I can point to multiple threads where this occurred) and so people are downvoting either due to the association with those threads, or due to a perceived need to protect LW's reputation.

It is possible that the arguments being made are simply weaker than those favoring infanticde and slavery, and they do seem to be somwhat weaker, but not so so much weaker as to explain by themselves the size of the downvotes.