This type of justification has always seemed very Stockholm Syndrome-y to me. This is not a valid or acceptable reason.
You tip in the US because everyone is complicit in the horrendous industrial relation laws.
Part of their vulnerability does come from near worthless job-injury/termination/severance pay because, on paper, take-home pay is far less than actual.
However, even in the jurisdictions that don't have a minimum wage exemption for tipped positions (such as Oregon), you're still socially expected to tip.
At this point, the only thing tips are good for is letting business owners pay staff less than what they would normally have to, which the staff doesn't mind because they get to evade taxes on cash tips, and they sometimes make more money than if they were to be paid a wage and didn't get tipped. The customer gets the raw end of the deal as they frequently overpay.
In food service, never say “cannot”!
It's not my role as a customer to support workers at a paper mill with lax safety standards because the workers won't go to OSHA, why should it be my role to ensure you have a livable wage because you won't go to to L&I to report wage theft/other practices?
And if they do award you back-pay, it may still be on you to follow through on collecting.
There is big structural barriers for the system to work in favour of employees that aren’t being paid properly.
You tip in the US because the employees are paid a sum that assumes tips are coming. You can pay less than minimum wage because the actual compensation comes from tips.
Of course, this is different in other countries...
And yes, 15% is standard for "acceptable" service and food. You can tip less if you really have a complaint, but with the proliferation of Yelp and Google Reviews, it's easy enough to avoid bad places.
On a road trip, that can be a little different, but...