MN power comes from women. Not just advertising. It has political influence.
The proposals, if they affect women in the way many here are predicting, therefore have major implications for MN.
If you can't talk about breastfeeding, pregnancy and childbirth, your general experiences as a woman - because it becomes deemed transphobic, what happens to MN?
Whilst this all might be a savvy business decision to make more money, the bottomline is that MN's entire existence could be at threat in the long run if they don't stand up now because of the nature of what people talk about. MN might end up in a situation where all references to mothers are deemed offensive. We might think this ridiculous now, but given the progression and manifestation of this, it would not surprise me either.
You say that Justine is defending users free speech, but actually gender critical posters speaking out in large numbers also protect MN and its business model too. Its mutually beneficial.
Political power comes from users. Even with her family connections, Justine wouldn't get a platform but for MN.
And yes personal beliefs do come into this, and given many posters have said they have only recently seen the inherent problems and conflicts of interests with TRAs, why shouldn't MN HQ also be in the same boat?