Earlier quoted context omitted.
Two differences that I see: A union is designed to protect your rights, forced arbitration is designed to limit your rights. Arbitration clauses are so ubiquitous that it would be almost impossible to operate in modern society while refusing to sign them.
A union may protect your rights, but they do ask for some in return - often the ability to work at non-union jobs. The point is, you're still "signing away your rights". You're agreeing that you won't do certain things that are within your right to do, as a condition to employment. Arbitration is ubiquitous because even at the cost of hundreds of dollars per hour arbitration is a lot cheaper and faster than going to…
You’re right but that’s not a great example of the rights you give up on joining a union. The right to work non union jobs isn’t particularly valuable except to non members and non members and people just starting their career are not the union’s concern. They protect the interests of the average member, so people for whom it’s a career, who have some years of experience. Those don’t generally work crappy jobs unless there’s discrimination against them.
Giving up the right to negotiate your own compensation would be a huge deal for any professions or jobs with obvious large differences in productivity and many employers. So you only see that at the bottom end. No limits on top end compensation. The Screen Actors Guild doesn’t say with this many years experience you must get paid this much, they say no one can get paid less than this.
With a single employer compressing pay differentials is a lot easier so you get what the average member wants, security of tenure, seniority based pay and promotions. If you want to negotiate something different go find another employer.