It depends how you define abuse. Acting entitled isn't abuse. Being demanding, isn't abuse. Calling someone a f b* is abuse.
If it's a situation where the police can be called, because an offence has been committed, then it's abuse but the server doesn't have to tolerate that and any good employer would back their employee on that.
When working as cabin crew, retail worker, barmaid and other roles, I found most people to be respectful. But then again, I am very passionate about great customer service and tended to be in control of the situation by setting the right tone. I believe that as humans, we copy the tone and attitude of those speaking to us. When I am a customer, if I go to a shop and say hello to the cashier and get ignored, no please or thank you, then I definitely won't say thank you as I take my change and leave, I will just walk away, treating the server with the insignificance that they treated me with.
There were instances of revenue protection staff being assaulted, which is wholly unacceptable but there is an element of confrontation to that role and similarly to you receiving police training, they were trained in avoiding the situation escalating to violence and how to remain in control of the situation.
GP surgeries tend to be calm places, despite the stress that customers/service users are under. I could hear a pin drop in my GP practice waiting room. It's not like an emergency room where there are people who may be drunk/on drugs etc.
I even find receptionists at maternity hospitals to have an essence of rudeness about them.
It's an NHS thing I believe, as private hospitals know that each patient is a customer and ultimately keeps them in a job, so behave accordingly. I cringe with embarrassment when someone appears on a quiz show and they are asked to state their occupation and they say "I work in the NHS....as an administrator"...as though that makes them the pinnacle of high society. We need to stop all of this hero worshipping the NHS and ignoring their failings. They do make failings and they do neglect patients, I have first hand experience of this. We need to stop this "hero-worshiping" delusion of anyone who has an NHS lanyard (notice how they wear it, even when not at work?) and "Key workers" (bawk). No one is more important than anyone else because they work for a certain organisation.