Because not all the benefits of membership are excludable. Unions that hold employers accountable to following labor laws and safety regulations benefit all employees, same with annual raises, removing abusive managers, better benefits, overtime pay [1], etc. etc. Some benefits are excludable for sure, a union isn't going to fight a non-members wrongful firing case.

[1] Some unions manage to get payroll benefits for just union workers but it's vanishingly rare because it just pushes workers to the union if they don't give it to everyone.

"Some benefits are excludable for sure, a union isn't going to fight a non-members wrongful firing case."

This is absolutely false. These are just a few anecdotes but there are several

"An arbitrator in 2007 found that teacher Alexis Grullon had victimized young girls with repeated hugging, "incidental though not accidental contact with one student's breast" and "sexually suggestive remarks." The teacher had denied all these charges. In the end the arbitrator found him "unrepentant," yet punished him with only a six-month suspension."

"In 2016 and 2017, Poway Unified School District officials found that Westview High School coaches Derek Peterson and Tim Medlock sent inappropriate text messages to underage students. Those officials found that they violated school policy and in response, issued each of them warnings. Both men continue to teach at Westview High."

https://www.wsj.com/articles/SB10000872396390443437504577547...

https://voiceofsandiego.org/2019/08/15/how-do-misbehaving-te...

Are either of these cases of unions aiding a non-member, which is the topic of the sentence you quoted? I can't read all of the first one—which is an opinion piece anyway, as is the second—but the second doesn't seem to be about that.

At any rate, this, from your second link, is insightful:

> For Medlock and Peterson, it wasn’t necessarily the union that protected them. It was the district, which said they’ve been disciplined enough.

You wouldn't believe what districts cover up or ignore, even if the union's not a factor. It's routine.

Why is a union necessary to enforce labor laws and safety regulations? Can't individual employees report such violations to the government even in non-union shops?

It's much riskier and costlier for employees to report that kind of thing, in a non-union shop.

Union shop, if you're sure what you've been asked to do is a violation of rules, you tell your boss no, then to fuck off if they try to pressure you, and you'll be totally fine. If you're not sure if something's OK, you have the union as a resource to check with, not just other managers working for the company (whose interests may not be aligned with yours, and even asking questions might be risky).

Non-union shop... good luck with that. You can go to regulators, but it's more effort, the process for doing so is something you'll have to figure out yourself, and it's a case where even if you're right you can end up having a rough few months or even years getting it all sorted out and being fairly compensated for any e.g. retaliation that happened.

Ideally, you want reporting problems of this sort to have a low and consistent cost for the person reporting it, not a high and very uncertain cost. If you want effective enforcement, that is.