It's not even about the ship itself (although I do think it's delusional to go beyond the jokes and actually believe it was written as a secret romance all along) but the way they distort almost everything about the story and characters to fit their shipping agenda.
I will mostly talk about a completely biased and inaccurate youtube video that is, let's be honest, more about glazing and victimizing Sasuke than the ship itself. T
First this person claimed that people were actually wrong and Naruto is the genius who inherited every of his skills from his parents while Sasuke is the hard-worker and underdog. And yeah this sounds ridiculous written like that but because of her and other narusasu shippers, people are now starting to buy into this false narrative. Even though Hagoromo said on the page that children don't always inherit the gifts of their parents when he was directly comparing how similar his son Ashura and Naruto are to each other. And even though Kishimoto himself described Sasuke as a natural genius AND admitted that Naruto is inspired by himself as he was struggling academically in school and used to be seen as a failure until he became a successful mangaka.
Another thing this person lied about is that Naruto called Sasuke a brother because he apparently didn't understand familial relationships since he was an orphan but that Sasuke never called him a brother because he understood it was "romance" between them and not brotherhood. When actually not only did Sasuke bring up Naruto's words about viewing him as a brother at the end of the manga and admitted he was right, he even compared Naruto to Itachi and said Naruto was walking in front of him like his brother used to.
Finally this person claimed that Sasuke is feminine in order to argue he's written as Naruto's love interest (which is problematic in itself because you should not need to make a male character feminine to justify a romance between two men, like why can't the two men be both masculine) and that him looking like his mother is meant to tie him to femininity. Even though Naruto literally has Kushina's face and also acts a lot like her. And even though it's displaying an ignorance of East Asian beauty standards since someone who looks like Sasuke would be considered the embodiment of masculine beauty in Japan.
And I could bring up many other examples like that of this person twisting the story, if not outright lying about it. But honestly it's telling. Those people always justify themselves with "it's my own analysis" but if you need to misrepresent the story and characters for your analysis to make sense then maybe your analysis is wrong.