Part of the issue is that the public in general seem to think that because serving someone 16 or 17 alcohol with a meal, or anyone over 18 is allowed in law, the server is obliged by that law to do it, and that's not the case.
I've indeed dealt with people who were going to 'report' me (to who I don't know) because they thought I 'had' to serve them as they were over 18, had to as in obliged by law to do so. That's not the case.
In the course I did to get my personal licence, it was mentioned that you can face issues around your license (personal and premises) should you serve someone who's behaviour is already aggressive (even verbally) who then goes on to cause an issue where the police need to be involved - because it's seen as irresponsible to serve someone a substance that is known for changing behaviour, lowering inhibition and causing aggression, to someone who is already behaving that way - even if they're not drunk.
As I said in a PP, for the licensee and the server, it is not just about keeping within the law, it's about keeping the alcohol license you have paid a lot of money for, and that makes you money.
The general public don't tend to know the requirements and restrictions around licencing, because they don't need to, but they are very much there and real concequences exist from breaking them.
Before lockdown a fairly local place lost their license, they hadn't done anything illegal, the holder had posted some questionable things on social media, and been involved in some issues that were morally wrong. The licencing team objected to the license on the grounds that the holder wasn't a fit and responsible person to hold an alcohol license. None of the issues were directly around alcohol, but with a revoked license, the business closed.
I think it's wrong, personally, to load other people's behaviour when they drink, onto someone else and expect them to take the concequences, but it's a more effective way of controlling it, as you're talking about loss of jobs and livelihoods, and as very little or no responsibility is placed on the person who is demanding the alcohol - there's no concequences for them - people blame the servers and licensee for being overzealous and jobsworths.