You make some big assumptions about my politics here. Believe me, I've got plenty of 'distress' for employers. None of this changes the fact that if you know that service workers are grievously exploited and you choose to have them wait on you while not compensating them, then you are also committing an immoral act. You and the employer then have something in common: you both know that the worker ought to be compensated fairly for their work, and you're both refusing to do it.

Am I absolved of sin when buying clothing that I know is produced in a sweatshop because 'well, the employer really ought to improve working conditions, but that's not my problem'?

The employer first exploited the worker, then you went in, benefited from their labor for free, directly reducing their income, supporting the business that exploits them while not supporting the worker, and somehow, your hands are clean?

You could choose to simply not give businesses who don't fairly compensate their workers your money, but instead, you give them the cost of your dinner and reduce your server's hourly wage?

If people want to reject tipping culture, they need to reject businesses that practice it, not fund them.