This was such a simple problem to fix for United. They offered vouchers for people to volunteer. No one accepted. So keep raising the offer until 4 people accepted. Problem solved.
I'm honestly flabbergasted by how idiotic United was in this situation. Was a few hundred/thousand dollars in savings worth the negative PR they got out of this whole ordeal? Every consumer knows how shitty economy flying is, especially on United, and would easily sympathize with the consumer who bought their ticket fair and square.
Instead they chose violence.
I will never fly United Airlines again.