I don't care about the right of people to choose in this game. The problem is that forced party membership damages the game aspect in a number of ways.
First, it damages recruitment efforts. Second, it confuses new members, forcing them to make an early decision too quickly. If you check now, most new members start off as undecided or independent, but end up choosing a party within a week. Third, forced membership does nothing to "advance" the game in and of itself. Fourth, it reduces the ability of new members to create their own party. It forces them to join an existing party and only then gather a movement to break out of the rigid and "strong" party structure you envision.
It's just a bad idea if what you want to do is make for a more fun, more free-flowing game.
My point is much more broad based than that single issue; that was just the particular motivation for posting this.
You're also wrong on a lot of the other points, but I'll deal with that in the other thread.