Irl, culture. 15% is becoming an insult but is still normal or acceptable most places. If you ever want to return to a restaurant and not have your food tampered with its best to keep with some agreeable norm. At 10% I wouldn't suggest being a frequent visitor anywhere for your health and wellbeing. To zoom out a little, there's been no country I have lived in where the culture was 100% agreeable even to the majority. We're all policed in some way or another by it.