If you're rich enough to consider an extra 20% on a meal "marginal" then good for you. I am too, at this point in my life.

But we need to recognize that as a privilege. For most people (including me, ten years ago) that's absolutely not marginal. Most people are having to budget and count their money carefully even at amounts you are privileged do dismiss as having no relevance.

Having the privilege of wealth is fine, up to a point. Being so wrapped up in it that you don't recognize it as a privilege is not fine.

Where I come from tipping means rounding up to the next round sensible number. That is marginally more expensive.

15% to 20% as customary in the US is anything but "marginally more expensive".