Stallman Attacks Gates, Microsoft, & Charity Foundation
Only because there aren't a group of idealogues running around providing free plumbing, electrical, engineering, architectural or carpentry work. Those trades would be screwed if there were.
You're also missing another point, which is certification. Most of those trades require you to be certified before you can practice them for money. Another example would be the law. The law is free... Anyone can learn about the law. If you want to practice law, you need to pass the bar and be licensed. Same with medicine.
Open source & Free software are great things, but to pretend they are something they aren't is disingenuous.