Sure, in battle it's ok to come to a mutual agreement with your foe about how you'll conduct that battle.

That said, "unionizing" is not battle. Nor does the Geneva convention apply to civil wars.

What do you make of the history of corporate actions that led to unions in the first place?

Yes. Luckily, the law prevents overreaching employers from firing employees that insist on their rights. The alternative is a return to 18th century factory conditions, and I'm sure even you don't want that.

A company is never on your side.