The United States allows each State to set their own standards in regards to alcohol sales and the identification required to demonstrate proof that individuals are of age to purchase alcohol whether in a liquor store, a grocery store, a retail store, or a restaurant. The fact that the identification law isn't consistent from State to State, from county to county, from store to store, is part of what makes America great, because often establishments can set their own standards as to what makes the most logical sense for them and their customer service. However, in certain States as well as in particular counties within a State, the State or county authority may designate very specific standards of identification that will or won't be acceptable for the purchase of alcohol. Further, those States or counties may take perfectly valid forms of identification such as a military ID or a passport or a foreign driver's license or an out-of-State driver's license and stipulate by law that these forms of ID are not meeting their particular requirements. Further to this point, and especially galling, there are some counties which make it a policy that all individuals, no matter their age, must show valid ID to purchase alcohol or the respective sale will not be made.
As always, when counties and States pass laws they ostensibly do so under the guise that this will protect the community and its citizens. This would presuppose a couple of things, one being that before these laws were passed, somehow the community was in some sort of greater danger and further that asserting the arbitrary authority of the State or county against a mere individual is always a good rule of thumb. The fact of the matter is, if a person wishing to consume alcohol is of age, the laws that mandate that only a certain particular piece of identification is acceptable, serves only the purpose of making it more difficult for particular peoples within a community to purchase alcohol. For instance, not everyone has a car, not everyone has a valid driver's license, not everyone is a legal resident in America, not everyone carries ID with him 24/7, yet typically we know that those that lack a driver's license and consistent ID on their persons, are invariably those that are underserved by their community to begin with, so strict identification laws are really, in essence, just another way of harassing or interfering with an individual's pursuit of happiness and general freedom.
Additionally, and very important to the whole format of having to constantly display one's ID to employees of establishments is the meaningful fact that your driver's license is the very road that an indiscriminate person could easily take advantage of. Your driver's license has your real and full name, your real and full current address, your real age, height, weight, and a unique identification number assigned just to you. All of these are the very tools that nefarious persons would love to be able to get their hands on in order to perhaps harass you, harm you, stalk you, or to become you. So that you can easily state, that the routine handing over of your ID to people that have no real justification for having it, is a potential and real menace to your own health and safety.