YSK that in US, getting carded for buying alcohol is not a personal insult to you, but required by the establishment by LAW

This is apparently not common knowledge. Do not be insulted if you have your ID checked for buying alcohol.

The restaurants are not doing it to spite you. They're doing it to not go to jail. It is in every state's law in some form that everyone who purchases alcohol must present ID. Depending on the state and the type of establishment, there are some exceptions on a case by case basis: sports stadiums or theaters not checking IDs if you look older than a certain age because of the congestion it causes or because the beer guy has a 40 drink tray in his hands. But these exceptions are written on the liquor license and are not universal. If you're just going to a restaurant, bar, store or club then expect to be carded.

Each state has a Liquor License Compliance or Alcohol Beverage Commission that do random compliance checks. These checks take many forms: simple visitations to the bar, paying minors to go to bars with either their own (underaged) IDs or with fake IDs, roaming around during that state's prohibited times of serving alcohol etc. If a bartender or waiter/waitress is caught during these checks to do something unlawful: serving alcohol to a minor, not checking IDs, serving an intoxicated person alcohol, allowing drug use on premise etc, they have the authority to arrest that server, close the business down on the spot, and issue citations to the owner, manager, and staff involved. The owner then receives one strike against their liquor license, and if they receive a subsequent strike then they may never NEVER operate a liquor establishment.

It is serious business for us to check your IDs. We just want to serve you and not go to jail. For the time you get in my face about having to see your ID, you could have just shown me your ID and already have your drink.