My father is a plumber, my father's brother is a plumber.
It's decent money. Much better if you own your own business and are a go-getter. But I'd consider both of them to be middle-class. Some companies offer better benefits and salaries than others and there's always union work, but I'm not sure if it's as lucrative as everyone thinks it is.
I work in IT administration right now. If I could make what I make here just laying pipe 40 hours a week, I'd almost consider it. Just because I know most of the people in the trade right now are losers and good men should always be able to find work SOMEWHERE. But I don't think I can. After 5 years, I'm making more than my father, a master plumber for about 30 years now.
It's blue-collar work, which means you're gonna break a sweat every day and you're paid by what you do moreso than what you know. You can "work your way up", but it takes time. If you wanna make money in a blue-collar field, you're eventually going to have to go into business for yourself and hire people to work under you. Otherwise you're just a wage-slave like everyone else. But that goes for ANY job.
Bottom line...if you don't WANT to do it, then don't. You're not passing up any "huge opportunity". You're not going to look back in 20 years and say, "My life would've been so much better if I had become a plumber". And if for some bizarre reason you do, just go to trade-school at night and learn it.