This is closely related to one's self-assessment and the question of being right and doing right thing.

If one is right, stand up do not matter. If one is wrong, they help greatly.

You say : why should I suffer for unprofessional and weak team member who is wrong?

But you forget to note that the same person could be right sometimes and doing great things and be utterly wrong and solving wrong problems some other times.

Edit: a also wanted to add, that input from peers and peer pressure is not to be underestimated. Management is be wrong as often as any of us.