As one of the few actual journeymen commenting in this thread, let me clear up one common misconception. Just because guys get laid off, doesn't mean they are useless in the trade. Anyone who has ever worked in highrise construction will know that there are literally hundreds of plumbers and electricians working on those jobs. If a company has all their eggs in one basket, such as the high rise condo market, they will need lots of workers. Problem is, once that job is done and you don't get the next one, how the hell are you supposed to keep 100+ guys busy? That is why there are mass layoffs, and it will never change. The same goes for govenment projects, universities, airports, etc. It isn't like there aren't other companies trying to get the same work. A company that has 100 journeymen electricians may layoff 95 of them when they lose the work. I highly doubt that all 85 of those guys are useless.
I don't know as much about the residential side of things, but I'm sure it is the same. Probably more useless guys in that side of the trade, in my limited experience. Sure, the useless guys can hang around when the construction is booming - unloading trucks, bending conduit, pulling wire... But, trust me: I know many highly skilled guys that have been laid off at some point due to the economics of contstruction.
The only real recession-proof trades are the service based ones like elevator mechanic, refrigeration mechanic, and as I said earlier, stone mason. Anybody getting into a construction based trade like electrician, plumber or sheet metal has a high risk of being laid off at some point, regardless of your skills and ability.
And, as Jennifer mentioned, there is indeed a ton of political bullshit in trade unions. Anyone who thinks otherwise is obviously not a member of one.