Changelings are no longer a team antagonist.
The other antagonists you listed are team antags, and are expected to cooperate.
It has been policy on Bee that lone antagonists don’t have an obligation to complete their objectives. Roll Traitor and simply want to lurk in maint abducting people to brainwash? That’s fine. Roll ling and want to use the regenerative powers to survive exploring space? That’s fine.
If you’re a traitor, you can kill other traitors for their telecrystals to boost your own. That’s a bit mean, but allowed.
What’s under discussion here is a player seeming to go out of their way to ruin the round for other antags, in a way that breaks immersion and RP (confirmed enemy of the corporation working with security). It didn’t give them any benefit, since they didn’t bother to complete their objectives.