I never was much of a union guy, I still have lots of issues with how the laws are written, and the transparency of some of the corrupt leaders.
But, back in the early 90's, I worked for an airline (America West) that was about 7 or 8 years old, and we started having union organizations. There were some pretty dirty dealings with the flight attendant union, and the union didn't get voted in. Mind you, transportation companies work under the Railway Labor Act, and under that, if you vote in a union, you can never go non union again, you can decertify and switch unions. Anyway, the company went Chapter 11, and the original founders of the company, who were liked and respected were replaced. The new CEO basically was the antichrist (he still is, he now the chairman of Frontier/Spirit Airlines, and Wizzair in Europe), so, eventually the flight attendants and pilots and mechanics and all other line positions went union, they had to so their jobs would be protected in case of a merger. AWA basically took over USAirways, and because of the union, the flight attendants were treated fairly for seniority, the pilots, not so much, long story. A few years later, US merged with American, and again, because of the union, seniority was integrated, and everyone kept the adjusted level of seniority. Seniority is the most important thing in the airline biz, the more seniority you have, the better lines you have for flying, it is a move up from being on unpaid reserve up to regular schedules, then to widebody international flying, you only get paid when you are flying.
Without the union, my friends would have all been "stapled" to the bottom of another company's seniority list, a massive demotion.
As for Amazon, good for them, I hear horror stories from there, and have read a lot of lawsuits as a result of how the treat their workers. When you have good management, you don't have unions, when you have bad management, you must have unions.