I've seen / experienced several train-wrecks caused by flat / self-organizing teams (see my sibling comment). In those catastrophes, I would have been glad for almost anybody to take on the role of team leader / manager.
So I'd be reluctant to assume the argument for structure is motived by personal ambition.
I've been in the opposite situation once and it turns out upper management wasn't really fine with a self directed team without a designated manager / leader.
Granted they wanted to introduce changes and needed someone to enforce that. We ended up sort of pushing in unison for the person who we thought would be the best and he did a fine job managing that team.
So I'd be reluctant to assume the argument for structure is motived by personal ambition.