So basically we have some vague unsourced stories about unions deliberately sabotaging products or services, but nothing concrete with which to make these claims of "why haven't they learned" or whatnot.
A couple things about unions. First, they're not the ones hiring the employees, that's the company. So while retention of employees is a union issue, if you have a factory full of assholes, that speaks more to there being inept management (especially in the hiring departments) than anything else. Secondly, it's not in the union's interest, pretty much ever, to make products worse deliberately, as everyone here knows. Guess what, the unions know that too, and have known it for pretty much the entire existence of unions. Their main bargaining tool tends to be work stoppages which hurt the company without directly hurting the consumer.
But of course krellin is also right here, the unions do drive up prices compared to non-union labor. But regardless of how much factory workers make, the US has by far the grossest disparity of income between CEO and median employee salary. No other country comes close. So the prices aren't all factory worker salaries, as some anti-unionists would have you believe. Which also kind of messes with that idea that higher taxes on the wealthy would lead to them moving their companies overseas...no other country can give the top dogs the compensation that the US can give, even if they were to get taxed more than they currently are. Sorry, tangent.