You're not being scammed in the US. You're given the ability to give immediate feedback on the service you received by adjusting your tip amount. What I don't

You're not being scammed in the US. You're given the ability to give immediate feedback on the service you received by adjusting your tip amount. What I don't understand is people saying they are "forced" to pay extra... Why would raising all the prices of the food 15-20% to make up for lost tips and actually forcing you pay that be better? Then you don't have the option to pay less if the service was bad.