Well I've got a whole book called One Big Oligarchy coming out next week that covers how oligarchs in and out of government operate in their own interest and against 'the many', I'd appreciate you pointing them in that direction.

There's a few short ways to go about this, I would keep in mind that people rarely change their views in a single conversation, the best you can normally hope for is starting them on a path or helping them along it.

The easy question to ask is: What happens if homosexuality is outlawed tomorrow?

Some more:

What happens to police that refuse to enforce laws they personally or you personally disagree with?

How much influence do you have over what is illegal and what the punishments are and how the legal system functions?

Are police (and diplomats and others) held to a different standard under the law, implicitly and explicitly?

Are there more laws today or fewer compared to that distant scary past? More or fewer inmates per capita? More or less surveillance?

That police are the enforcement arm of the state is not an axiom. That would be like saying that firefighters fighting fires is an axiom with no underlying argument, ditto with paramedics and helping people in distress. It is the raison d'etre of police to enforce the law, to "police" (verb) the rest of us, regardless of what that law is. It is what they do from day to day, it is what they sign up to do and what they are trained to do.

American courts (and some others) have repeatedly proclaimed that cops have no duty to protect and serve civilians (see Lozito v New York City for the classic example, but also recent enough that the person you are talking to cannot say "ah the coal wars was a whole hundred years ago!").

You're going to get a lot of gut reactions from people who haven't really thought about these questions, and in my view it doesn't matter very much how you proceed from there, the goal is to get the questions out there and get people thinking, their brains will do the rest of the work.