His friends would likely be in shock. Sasuke, for instance, might be deeply affected as Naruto is his closest rival and friend. He could initially be angry at Naruto for being so reckless, but then feel a deep sense of loss.
Another reason might be related to his pursuit of power. If in the fanfiction, Naruto is constantly facing stronger enemies and he believes that his current strength is insufficient to protect those he loves, he might attempt to sacrifice himself in a desperate attempt to gain more power, like through some dangerous and forbidden jutsu.
One common theme is extreme despair. Maybe Naruto has lost all his friends in a tragic battle and feels like he has no purpose left. Another theme could be self - sacrifice taken too far. He might think that by ending his life, he can save the village from some great danger in a way that doesn't actually require his death. And sometimes, it's about the psychological toll of being the jinchuriki and all the hatred he has faced throughout his life finally getting to him.
On one hand, it humanizes him further. Everyone has dark moments, and seeing Naruto in such a state makes him more relatable. However, on the other hand, it can be a bit jarring for some fans who are used to his upbeat and determined self. It might also lead to a deeper exploration of his character's psyche, forcing fans to think about what really drives him and what his true fears are.
One possible reason could be the burden of his past. Naruto has faced a lot of hardships and the memories might be overwhelming him, making him want to be alone. For example, the loss of his master Jiraiya might have left a deep scar, and he might feel that isolating himself is the only way to deal with that pain.
Maybe he feels a sense of guilt. For example, if something bad happened in the village that he blames himself for, even if it wasn't really his fault. He could exile himself as a form of self - punishment. He has always been very hard on himself when it comes to the well - being of the village and his friends.
In fanfics where Naruto attempts suicide, it could be due to extreme loneliness. He has often faced isolation in the original story, and in some fan interpretations, that feeling could be amplified to a point where he sees no way out. Another reason might be failure. If he fails in protecting his friends or achieving his goals in the fanfic's alternate storyline, he could feel so despaired that he contemplates suicide.
It can have a negative impact on some fans. Naruto is a character known for his resilience and positive attitude in the original series. So, seeing him attempt suicide in a fanfic can be quite disturbing for fans who look up to him as an inspiration. It may also make some fans uncomfortable as it goes against the core values of the Naruto universe which promotes perseverance and hope.