I get it to an extent. If someone is slurring and sloppy drunk, serving them more alcohol is irresponsible. You don't know what they're going to do but you do know their decision making is thoroughly impaired so cutting them off makes sense. Some people act almost perfectly normal even when drunk though so it's not like they can be responsible for everyone they serve.

After one drink, I wouldn't question shit because you can barely feel it. This chick had way, way more than a single drink. If I'm going out, I have 2-3 ciders max depending on the size that's served and how many hours I'm out and about. The idea that you can't have any at all and still drive seems like it's coming from people that don't drink at all and don't know how it affects people.