I don't doubt the job is tough and physically taxing. I don't think many think that. The mentality is typically along the lines of the skill required to do the job is low (There is no arguing that) and the union mentality is archaic (which it is). If you run a comparison of the Big3 to the Big3 in Japan, they all staff about the same.
Ford and GM are around 2ook employees. I can't find any good data for Chrysler, Jeep, Dodge, Ram since they all seem to be considered separate companies, but the numbers I did see indicate they are probably around 150k to 200k. Obviously those three are unionized. The Three that aren't Unionized for comparison are Toyota, Nissan, and Honda. Toyota dwarfs the others in size with over 330k employees. Nissan and Honda are both around 200k. So for size comparison all things are equal, except Toyota. Average pay for the foreign companies is 30/hour. Average pay for the US workers is 28. So the argument that non union works in small companies, but not large doesn't work. The difference is total cost for an employee. In the US it's around $68/hour. That covers benefits, hourly pay, and covering future benefit costs. I can't find any data that specifically says new hires in the us plants get a pension so I don't know if that's playing into that number or not. The average cost for a foreign employee in the us plants is $48. Numbers don't tell the whole thing obviously. Employee satisfaction and turnover rate speak volumes about a company, but that data isn't readily available. The complaints and reasons I hear justifying the union just don't matter anymore and in the end, they are being held back from opportunities for greater than what the union gives.
The problem with the union is it's a 1950's mentality in employment practice, status, and benefits. In some areas things have definitely gone backwards over the last 65 years. The average length of time that an employee stays at a job in the US is 4 years. This is driven mainly by the employees. It's a competitive market (when not in an economic slump) and you can greatly benefit yourself by changing jobs. I'm living proof of that. I changed a job 4 years ago as well as a year ago. Between those two job changes I tripled my income. Show me that happening in a union shop. It's an opportunity that you lose out on by thinking it's the 1950's and an employee and a company stay together for a whole career. As an aside, the average length of tenure in a job globally is around 9 years. The US has one of the lowest. The countries with the highest are also mostly socialistic countries. The other reason the UAW is archaic is that is completely ignores the day and age we live in. You'd think with the mentality of UAW bosses that we live in a day and age where people get their news from the newsboy standing on the corner. That once inside the plants there's no means of seeing and recording what is happening. That companies will put worker safety at risk. You can't take a crap now without someone recording it let alone a company pulling off some horrific treatment of its employees.
All of this shows that the UAW is an added burden on the company with no added benefit and holds back it's employees. This is what 89% of the US working population understands and sees but 11% don't (Assuming all union members enjoy being in a union).