Sounds a bit like mandatory donations. Not much of a donation then eh?

Tips isn't a donation, it is coerced from the customer since they know many waiters will make a fuss if they don't tip.

If the service is acceptable, you tip ~20% (still okay to round down a few cents). If the service is bad, you don't tip 20%. Usually, if you complain, they will give you some part of your meal free or otherwise provide an adequate remedy, in which case you still tip 20%. Otherwise, it's okay to tip less. You can leave 10%. You can even leave 0%, but don't expect to come back. A sincere apology and attempt to remedy at least deserves some tip.

This is what’s some times internationally called a “service charge”, not a tip. It's part of the agreed price, not something I voluntarily add. The "price" is what I can pay and still return.

It’s effectively a part of the agreed transaction. I understand the mechanics of it, but it’s extremely weird to me (who isn’t American). I’d be fine with service charges of almost any level. Also if it said “service charge is 30% - please let us know if you aren’t happy with the service and we’ll remove it or compensate you”. That’s fine.

What’s important to me is that it’s on the receipt.

I wonder how Americans feel paying 0% tip without complaining in Europe (I wouldn’t ever complain and possibly not come back).

It’s a different culture. In America, “the customer is always right.” That’s not literally true, but the general approach is that the customer, the one bringing the money, is the boss and his reasonable requests should be hastily fulfilled. That authority is reflected in the power to set the tip. In Europe that is emphatically not the case, especially outside upscale establishments. America is actually drifting toward Europe on this point, with millennials being less willing to complain or to penalize in the tip. But a wide gulf remains.

In some other cultures, good service is considered more of a moral obligation. The shame of providing bad service and of being known for it keeps waiters and their managers on their toes. Different culture.