It's pretty clear that as union membership increased in the beginning of the last century it played a key role in the rise of the middle class in the US.
Unions played a big role in getting better workplace environments. That battle was won, and with OSHA, 24/7 media outlets, and social media, those environments will never return.
The "rise of the middle class" is MUCH more directly attributed to capitalism. I'll explain...
Conversely as union membership has declined and public policy has become increasingly anti-union (beginning with Reagan breaking the air traffic controllers union) the middle class has seen wages stagnate, wealth decline and inequality and upward mobility in the US according to Joseph Stiglitz now lagging behind I believe all other western nations.
Unions declined because they got beat in business. A union-made product is more expensive, so it must be better to be worth it. When it isn't, they get creamed in business. That is just the economics of it all, corporations need to lower costs to compete.
You are lying when you say that wealth has declined. I read a report a month or two back stating that since 1970, with inflation accounted for, wealth has risen something like ~8% for the very poor, ~30% for the middle class, and ~256% for the rich. So while the rich are much better off with their income, everyone is.
Still, income/wealth doesn't tell the whole story. The standard of living and quality of life is still rising, due to capitalism. While you claim wealth is decreased, in relation to the cost of goods it has not. You cannot notice it from one year to the one before it, but you would be blind to see how society has moved forward over, say, a decade.
A computer ad from a decade or so ago:
For that price today, your computer is 50x better.
A "good" digital camera today would have cost ~$6,000+ in 2000. Today it is $100.
Today we have iPads, and wireless internet, and televisions in 1080p for a fraction of the cost. Everything piece of technology you use is cheaper than it ever was. Consider that.
The lifestyle Americans live is so superior to most of the world, it's not even funny.
Unions serve a really important role in the balance of wealth and power in any civilized society in my opinion and if they are done away with completely then we will be even further down the road to becoming a society that looks more like present day Mexico. Where wealth is everything and everyone else can suck it.
No, they don't. If they were the case, cities with a big union presence would be doing very well right now. They are outdated dinosaurs throwing a wrench in the globalmarket to try and hold onto their piece of the pie. They will lose that fight unless there is an artificial boost (aka the Democratic Party).
Union members threaten that we'd turn into Mexico or some third world country, and that is Grade-A bullshit. Capitalism is constantly creating wealth, and to create more and more wealth you need to sell goods. You can't sell goods to the very poor. Even if the rich had the power to turn the middle class into serfs (and they don't), it wouldn't even f*cking be to their benefit because their sales would decrease.
Honest question, have you every taking a single economics class?