As a person of colour, I understand what you mean from a perspective of race. 9 times out of 10 a white person, male or female, will not hold the door for me and another person of colour will. I do not think that they are overtly being racist, but that it is an in-built behaviour that has come about through social conditioning. It is something that is hard to explain because most of our behaviours as humans are hard to explain. They are hard to explain because we are not behaving consciously most of the time. We are simply going through the motions governed largely by what we were taught is appropriate behaviour in that situation.
Growing up, my mother taught me that it was my duty as a man to hold the door open for a woman. That if a woman was directly in front of me, I should walk a bit faster to get to the door before her and open it for her because that is how a gentleman is to behave. In her mind, she wasn’t teaching me to be a sexist but to be a gentleman. I don’t blame her or knock her for behaving this way as she came from a time when all men were expected to hold the door, pull the chair out, etc. As I have gotten older though, I am now torn every time I get to a door about whether or not I should or should not open a door to the point which I avoid doors altogether or will wait in the sidelines until I know I can enter a place through its doors without needing to have the doors held for me or hold the doors for someone else as I really don’t want to offend anyone and am too unsure about what could trigger someone.
I think that much of the aggression that you are seeing with men’s responses to stories like yours is not blind aggressive male sexism. Most of these men are coming from a genuine place where they are struggling with their sense of identity. “I was taught to behave this way and now I am learning that it is wrong. Who am I?” Anyone going through an existential reevaluation will most likely respond with aggression. That’s why it is my feeling that these situations are not only painful for the female but for the male. Not only do young girls need to be taught not to fall into the socially-defined female stereotype care-taker, but young boys need to be taught to fall into the socially-defined male stereotype of care-giver. (Not sure if those are the correct words but hoping you understand what I mean.) Men need to be taught that they don’t need to open the doors, pull out the chairs, etc. I have learned this as I have gotten older, that women are more than capable of doing all the things on their own unlike what my mother taught me about needing to care for a woman and that I should take the backseat and let them drive.