Don’t go straight out saying you want to abolish the state. Never deny it, but don’t let them bring it in as a “knockdown argument”. It shouldn’t be like this, but people don’t respect us if they know of our anti-statism.
Argue against specific things. Point out how regulation isn’t needed when it is relevant to what you are already talking about. Point out how the state messes so many things up. Point out the flaws in the reasoning of statists and Keynesians.
Then when they’re a minarchist (i.e. ideal situation), they should be convertable to full freedom. That’s how it worked on me, although noone was converting me, it was happening in my head, and through mises.org readership and posting here.
There’s also no example of a state that has only been constrained to defence functions for any significant period of time without soon beggining to sip from the poisoned bottle of statism, interventionism and corpratism (with the possibile exception of western countries in the 1800s but ooooh how the tides have turned!). Why wouldn’t defence agencies work together? That’s like saying phone lines or banks would never work with each other