the tragedy of rhaenyra and alicent is that they cannot ever truly see the other without destroying the foundations of their own self-image. rhaenyra cannot see alicent as a child married to a man old enough to be her father because that’s rhaenyra’s father. and the image she has of both viserys as a just and kind man and of herself as the beloved daughter of that man would collapse under the weight of that realisation. the resentment she holds against alicent would have to turn upon viserys. if she recognised that viserys treats alicent little better than a broodmare, she would have to realise that fundamentally that is all her mother was to him too. if she understood why alicent was disgusted by her marrying daemon she would have to see herself not as someone with agency marrying a man she loved who happened to be her uncle but as someone manipulated and groomed since childhood. the agency she clings to, which is so important to how she sees herself, would be revealed as an illusion. by extension she would have to see her family as one in which the familial is warped almost beyond repair. her self-image, so rooted in targaryen exceptionalism, would collapse.
likewise alicent cannot fully grasp why rhaenyra was so upset that she married viserys because she would have to fully see viserys not as the king but her friend’s father. she would have to face the horror of her life head on. moreover she would have to see viserys in her own father. for her to accept that rhaenyra is not selfish or undutiful for having affairs and trying to carve out whatever agency she can, the pedestal on which alicent places duty would have to be destroyed. she would have to realise that duty is only as important as she believes it to be, that it has no meaningful moral weight to it, and that all of her suffering has been for nothing. alicent tells herself that her sadness is a condition of her existence, as a woman, a mother, a daughter, and that by trying to claw whatever happiness she can from the world rhaenyra has turned her back on all of those things; she is the wrong kind of woman. if she could ever accept that rhaenyra had slept around and birthed bastards without judgement the core of alicent’s identity as a good mother/wife/queen would collapse. she would have to face the reality that nothing that happened to her was justified, and crucially that her submissiveness at every turn was not noble or good and was never going to let her win, but only trapped her further. every cognitive barrier she has built up to protect herself and provide some sort of meaning to a life in which she has only ever really suffered would have to shatter.
and they both realise these things to some extent, rhaenyra knows that viserys is flawed and fallible because she’s experienced his mistakes firsthand (and she is definitely aware of daemon’s violence) and in many ways alicent is so viciously judgemental of rhaenyra’s choices because she wants that level of freedom so desperately for herself, and they so clearly love each other still that they both want to believe there’s something good in the other. but they bury those doubts under layers and layers of cognitive dissonance so they don’t have to face deeply painful realities, because neither of them can truly see the other without destroying themselves.