Please read through this thread to see my struggle with this issue
I think you fell into the trap of trying to convince people that don't want convincing. They ask silly questions. Asking you to explain how a super rich person won't simply buy an army and take over has already been answered in their head. It is a gotcha question. It isn't sincere or genuine. Avoid those kinds of 'debates' like the plague. It will just wear you down. It is pearls to swine, my friend. Save your energy for people who really are curious.
It goes back to Stefan Molyneaux's example of getting the cotton picked.
"How will the cotton get picked if the slaves are freed?" Can you imagine trying to explain horseless carriages that mechanically pick the cotton 5 rows at a time to someone in 1860? They will just say, "Magical carriages, without horses? Nonsense! We would have to go get new slaves because your carriages wouldn't work!"
Stefan argues to stay focused on the moral argument.
"Slavery is wrong. When people no longer immorally desire to keep human beings as cattle to pick their cotton, then people will figure out how to get the cotton picked."
"State coercive taxation is wrong. When Uncle Fred no longer wants to have his nieces and nephews extorted under threats of murder to pay for his glorious national army then he and his nieces and nephews will figure out how to come together to protect each other from invading Mongolians, or whatever.
Don't get bogged down into their "explain the future" merry-go-round. They aren't asking 'buying' questions. They aren't undecided. You are talking with the wrong people.
Debate people who aren't sure of themselves. They can be won over if you can show the moral argument in a context that they can personally understand.