I think there's a massive amount of projection that goes on when feminists discuss issues like this.
Lots of people are simply not that used to examining ideas, habits, practices etc., as a thing in they're own right, worthy of examining dispassionately.
So when feminists do it, it's often perceived as an individual criticism of other women. When of course, it's nothing of the sort, it's an honest attempt to try and tease out all the interesting variables of why people do stuff.
But lots of people may suspect deep down, that their dearly-held individual choice, may shock horror, be influenced by the culture around them. Instead of accepting this as normal and human, as others have said, they feel ashamed of it, because the media is telling us all the time, that we are individuals in a vacuum and all our attitudes, decisions, choices etc., are made in that vacuum with no reference to anything else.
If you never question that idea, if you honestly believe that you make all your choices in that individual vacuum, `when someone suggests to you that you don't, this will upset you because
a) you feel you should be making all these choices in a vacuum and if you don't, then that means you're stupid and weak-minded and brainwashed
and
b) because you believe that shit, you will then perceive this person telling you your choices are influenced by stuff outside your imaginary vacuum, as in fact, telling you that you're stupid and weak-minded and brainwashed. This is projection on your part, because no-one intelligent thinks it's stupid and weak-minded and brainwashed to be influenced by the world and society you live in. They think it's normal and human.
In short, feminists saying that people are normal and human, is deeply offensive to many people.