you're not mark's friend, you're not his acquaintance. you're a fan, and the members are the ones who know him personally. they have every right to support their ex teammate, their friend, someone they've known for so long.
you don't have to support mark but remember it's not up to you to decide whether the members support him. they've been in a group with him for over ten years and they obviously know better what mark is like in real life