Your statement in very true in some locales, and not true at all in very many others. Teachers' unions are virtually nonexistent in the US South and Midwest, and only strong in the coastal blue states.
If "strong unions" made teachers lazy/bad, then we'd see poor performance in the strong union states like New Jersey, New York and California, and great teaching performance in the weak union states like Georgia, Louisiana and Mississippi. That... is not what we see.
It also presumes that unionization is the only way to rid yourself of the fear of getting fired. Unionization will alleviate the fear of getting fired based upon factors relating to competence, but another way to do it is simply to increase your competence. I don’t fear getting fired at all, partly because I know I’m competent enough that it’s incredibly unlikely, and partly because I’m competent enough that I know I could simply get another job if I wanted to.
I know that I’m competent, because I have enough experience to understand the problems that exist in my field, as well as how to effectively solve them. There is no randomness or luck involved.
While hard work can certainly allow you to capitalize on opportunities that come along, you have almost zero ability to create opportunities yourself. My current economic status is exactly because I randomly received an offer and worked my butt off to achieve success. Someone I know who is just as competent as myself isn't nearly as successful simply because he hasn't had the same lucky break. Bill Gates and Steve Jobs both worked hard, but both had random chance heavily weighed by who their parents were at birth which allowed them access to computing in a way that wasn't generally available.