"Maybe to add to the list - plural marriage, gay marriage, child marriage (hey, if you can beat them, why can't you join them?)."
Marriage is something that is part of the state in a similar way that a driver licence is. A libertarian wouldn't make the argument that the state should issue driver licenses to people who are unable to driver. A libertarian *might* say that you should not be required to get a licence in order to drive a car on public roads, nor be required to renew them every 5 years. Or libertarian *might* say that the state should require that people get something like a licence, but a person could get these from the private sector- and that this agent in the private would have bear some responsiblity if it's drivers weren't good drivers and perhaps "rewarded" in some way if it's drivers were expectional in that they were always polite, had lowest accident rates or whatever.

There is nothing ilegal about marriage- you could marry a cat or a tree- as long as there is not deception involved implies that marriage is sanctioned by the state. In other words if you owned a race track, you could make people get your driver's license in order to drive on your race track- there would nothing illegal about this as long it wasn't intended to be used to as a fake State issued driver's license.

"speed limits, smoking in public places, gambling, pornography, euthanasia/assisted suicide, abortion, censorship, the freedom to chose to be vulnerable to terrorism...."
On these you mostly right that these are issues libertarians would argue against on a state level- but there aren't federal laws against these [oh, except the abortion- there are federal laws on this].