First you need to prove all Amazon employees fit your stereotypes. Without that that's there's nothing for me to argue against. Your premise is flawed.

The only counter argument needed:

Some people work in Amazon warehouses because they're disenfranchised under served and desperate to not be homeless.

Anecdote: I've worked one union job in my life. I didn't work sufficient hours to get benefits but I was expected to pay dues. The union offered me no benefits and made plenty of statements about how I had to pay or they'd force me out of the job. I was young and didn't care, so I never paid and left when I found better employment. During my exit, my manager told me he was sorry to see me go but the union was going to force him to fire me soon anyway.

That single experience has left me no love for unions. Why should those who receive no benefits (I'm talking about things like medical) because they work less than a minimum amount be forced to participate? Why does a group get to string arm and individual who doesn't want to be part it? I'm not an amazon employee. I have no skin in this game. If I was working one of those jobs and had the hours, I'd probably have voted in favor. If I didn't have the hours though? Not a chance. Odds are the chunk the union would take immediately would be worth something to me and waiting for the collective bargaining improvements to hopefully (likely) come would not be a risk I'd be okay with.

So how many people working in these warehouses wouldn't qualify? I don't have the answer but I bet that's a well represented number of voters.