Aww,
The issue is not whether he can theoretically be Moshiach or not (that is a discussion on its own – refer to the closed thread: https://www.theyeshivaworld.com/coffeeroom/topic/mesichists-explained-by-chabadshlucha)
Rather, how it has been created as a tenet and essential part of Yehadus as a ‘movement’ on its own. There is no inyan on having to “follow” and declare one as Moshiach. Yes, you can believe whatever you wish as the Moshiach but to go to such an extent is sort of like it happened with the Shabsei Tzvi movement.