> I'm not an economist, but, free market theory favors lots of competitors, fully informed customers, and low barriers of entry which can be thought of as trying to keep consumer and supplier with a balanced amount of leverage (too much leverage on the supplier's side creates monopolies, for example).

That's a pretty strong argument against unions in the US, then, since (unlike in other countries) there's no competition between unions at an employer, there's almost no ability to deauthorize a union in practice (ie, choose a different union), and very high barriers to entry (very difficult to authorize a different union for representation in place of an existing one).

But the problem is that employers also have high barriers of entry (it's not easy to switch jobs, especially if you have to relocate), and there's usually low competition for blue collar work, since there's higher demand, which makes employers have overwhelming leverage. There are industries where that doesn't apply as much, and you can see that workers can get better compensation and benefits in those. Unions can equalize that leverage.

I do think that unions could also have too much leverage, but I think that finding a happy medium is a worthy legislative goal.