If you don't show up and present your case, the other side could win by default, not because they make the best case.
You're basically advocating for presenting a one-sided view to people and having them make a decision that way. This would imply that the union has a morally higher ground but I find that hard to believe as a union is just composed of people who are going to just employ the same tactics as Amazon if they could (albeit more limited at this time due to financial & structural reasons).
But the point is that in a sufficiently large corporation people mean shit and the company has disproportionate power over individual employees.
For example, in a small town with one large company there might just not be any other jobs.
The whole point of unions is to discriminate against the employer, to provide some leverage to employees to not be completely treated like shit.
If you are sufficiently large company you need to take correspondingly large responsibility and costs of maintaining that workforce.
In my view Amazon falls into both "sufficiently large" category as well as history of being shitty employer.
It is not a one-sided process, Amazon has already had great many chances to show they can do better but they chose to not use those chances to correct their behavior.
Like I said, the weakness in this argument is it presumes that forming a union is strictly better. Maybe it is in this case. Maybe it’s not. Muzzling any speech to the contrary isn’t great though. Both sides should be able to be full throated advocates of their position as long as they do so fairly and within the limits of the law.
Well, what do you expect?
If Amazon was innocent here they could just let people vote whenever they want and people would most likely not vote for union (because they would not have reason).
Instead they chose to fight against the vote which is not exactly inspiring confidence in their innocence, especially when they bend and break the law in the process.