One reason could be that it doesn't respect the original story's intention. The original Naruto story is about growth, friendship, and ninja skills. Harem fanfiction for Team 7 just throws in romantic elements that Naruto may find disrespectful to the real story.
It could be that Naruto hates how it portrays his relationships. He has a brother - like bond with Sasuke and a complex but pure friendship with Sakura. Harem fanfiction might make these relationships seem cheap or false in Naruto's eyes, as it changes the nature of their interactions into something more about sexual attraction rather than true friendship.
Naruto may not like the way harem fanfiction changes the focus from his ninja dreams. His main goal has always been to become Hokage and protect the village. Harem fanfiction in Team 7 context would shift the focus to romantic relationships which he may not be interested in at all. It's like taking away the essence of what he stands for and replacing it with something he doesn't care about.
Perhaps in this fanfiction, Naruto has been influenced by some external force. It could be a dark entity that has corrupted his view of Team 7. He might see them as a hindrance to achieving some greater, more self - centered objective. Also, it could be that Naruto has had some sort of personal revelation about his past and blames Team 7, or certain members of it, for things that he now believes held him back in the past.
Jiraiya was a serious shinobi with a certain code. Fanfiction might play around with that code too much for his liking. It could make light of things he held in high regard, like his loyalty to the Leaf Village or his training of Naruto. So that's a possible reason for his hatred.
Perhaps Tails feels that fanfiction undermines the hard work of the original creators. He might think that the official story should be the only source of information about him and his adventures, and fanfiction is an unwanted deviation from that.
One possible reason could be the way the villagers treated him as a child. They ostracized him because he was the host of the Nine - Tails. He was often alone and looked at with fear and disdain, which could have gradually built up his hatred.
One possible reason could be that the council often restricts Naruto's actions. They might see him as a potential threat or a wild card due to his Nine - Tails power. So, Naruto, being a free - spirited person, would naturally hate being controlled by them.
One reason could be that he was treated unfairly by other shinobi. If he was constantly looked down upon or discriminated against by his fellow shinobi, it might make him develop a hatred for them.
One possible reason is that Naruto is so focused on his ninja training and his goals in the shinobi world that he views Christmas as a distraction. He might think it takes people's attention away from more important things like self - improvement and protecting the village.
It might be due to the way their goals are presented in fanfiction. Naruto is often about protecting his village and friends. If Artemis's goals in the fanfic are in conflict with Naruto's, like if she's more focused on her own self - interest in the story, Naruto would hate her.
It's possible that the writer of the fanfiction has given Akeno a backstory or personality trait that directly clashes with Naruto's. Maybe she is extremely arrogant and Naruto, who is humble and believes in everyone's potential, would find that detestable.
It could be that Naruto has a different view of leadership than Sarutobi. Naruto might see Sarutobi's leadership as being too passive or too focused on maintaining the status quo. He, with his more energetic and revolutionary ideas, may resent Sarutobi for not being more progressive in making the village a better place for everyone, including himself.