Forget about the legal risks; how does that even work? If I don't think my coworker is doing a good job, am I supposed to secretly whip up enough votes to have them fired?
If you need to "whip up votes", this will say more about you than the person you think isn't doing a good job.
Borderline cases are trickier, but they are for managers too.
I can only assume that the actual firing process involves a lot of hushed talking followed by an approach to gaben followed by a discussion followed by a "sorry, bye".
One could in fact suggest that the flat management structure only works when there is exactly one clear owner of the company. Everyone can pretend that everyone gets a say, when it's clear to everyone who really has the final say.