Without force the unions can’t exist. It’s like a lot of things with government involvement: Unless you are forced to do it, many people, especially if money is involved, will eventually decide not to. So in order for the union to survive and have power they have to force everyone to join, everyone to pay, and everyone submit to its system whether they like it or not. What I see in this union vote is that people didn’t want to give up their autonomy to someone else. I think anything that asks citizens to give up some kind of autonomy - especially now - is going to incite people negatively.

Not a lawyer or organized labor person, but a favorable vote would turn the warehouse into a "union shop," where the union negotiates on behalf of everyone, member or not, with regard to wages and working conditions and collects dues from everyone, member or not. In my very limited experience, the union offers some benefit like vision coverage to encourage people to join.

IANAL but my understand is that it's the difference between the company being allowed to fire those individuals for not doing what is asked of them, and being legally required to negotiate with them.

They can, but members-only unions of the type most common in e.g. Europe have mostly disappeared in the US after the National Labour Relations Act 1935 made the current system possible.

On one hand I can see why it was attractive for unions to push for it, given how brutal anti-union efforts were in the US, but it seems to over time have had the effect of making unions focus on drives to win workplace by workplace and ignoring places they don't see a chance of winning a full-on unionisation vote.