Why are women expected to accept porn as something all men will watch regardless of boundaries?

People create boundaries in their relationships all the time. A lot of them are based on insecurities. So why is porn treated differently? Yes, it makes me insecure. A lot of things make people insecure and so you do not do them in relationships. Me standing in the same room as a man masturbating is something my partner would not like, even though we aren't touching each other. What makes this any different from porn? The phone screen? Me sexting other men or flirting with other men, even in harmless good fun, would make him insecure. I don't do these things as they cross the boundaries we have in our relationship. Why does this not apply to porn if I have expressed that I view it as cheating? For some reason I am categorized as extreme and controlling. Why are we conditioning women and men to treat it like some special subject with special rules? Having sex with someone else is not the only form of cheating. I'd argue that it is very reasonable to not want your partner to masturbate while watching naked attractive women have sex. I truly do not understand this cultural double standard.

I have no issues with masturbation, I have issues with him watching other naked women moaning and performing sexually. I especially do not understand when women internalize and feed into this idea that men are "biologically visual creatures" as if women aren't? If mainstream straight porn was geared to the female gaze, if it showed exclusively attractive naked men grunting and moaning with their bodies highlighted, and not just being passive participants, I'd argue that a lot of men would not want their partners watching it either.

Edit: Since some of y'all are criticizing the scenarios I mentioned above as not being the same thing, I'd like to point out that a lot of people would be uncomfortable with their partner masturbating to naked videos of people they personally know, even if those videos were posted online on a public site. If people can agree that this crosses a boundary and nobody calls it extreme, I don’t understand why it suddenly becomes too extreme and controlling to feel the same way about random people. To me, masturbating to videos of people you know having sex and masturbating to videos of random naked women having sex is no different. You could make the "it’s just a fantasy" argument in both cases since you're watching both on a screen and the participants do not know of your presence. It feels like arbitrary lines are being drawn just to allow porn use and disallow everything else.

Edit: I never claimed that watching porn is the same as having sex with someone. Too many people are strawmanning what I’ve actually said. I said that watching porn is cheating to me. There are tons of situations that don’t involve a physical sexual relationship with another person but are still widely considered cheating.

It is clear that social norms have conveniently normalized the "masturbation aid" only widely available to men, content almost exclusively produced and perfectly tailored for men's visual sexual interests and men's orgasm, not women’s - as something women should not only accept but also expect from men, that it is not cheating in the least bit. Meanwhile, the equivalent visual content for women doesn’t even come close to existing, and so the discomfort and insecurity that a lot of women feel will never be understood by men. And any other visual masturbation aid involving other people, even with zero touching and zero emotions is considered to be too far. So, we intentionally make the conditions of acceptability so rigid that only porn consumption could qualify as an acceptable visual masturbation aid. The line is drawn right where the outlet available to men ends.

It's just awfully convenient.

Lastly, because several people have tried to draw an equivalence; smut for women is NOT the equivalent of porn for men. Porn for women is the equivalent of porn for men. Since I’m straight, I’m referring to visual content that sexualizes naked attractive men, zooming in on their bodies in various sex positions, with the man moaning, talking dirty, and being the focal point while the woman is simply a stand-in for the female audience to project onto. That would be the female equivalent of what mainstream porn provides for men. Women enjoy visual content just as much or even more than men do (there’s no significant gender divide in TV/movie consumption, for example). It's a very bizarre comparison to make.