Guarding the US border is the job of the military, not the local sheriff. (DHS has failed to do this)
Where do you come up with that? Cite something in law that says that, or is this just another rant?
The Border Patrol, Customs and Immigrations, and Revenue Agents all patrolled the Border in years past. It has NEVER been a purpose of the United States Military, unless in time of declared war.
To say that DHS has failed to do this is ludicrous. Before there was a DHS, these agencies existed, and the same things were said. The military is prevented from taking a law-enforcement role by Posse Comitatus. Would you like to repeal that?
As for the armored vehicle, just about any state allows private ownership of them, As for the Machinegun, depends on STATE law, not Federal. In Georgia, you could own both. State law doesn't prevent mounting the gun, either. You used to see Jeeps with mounted 1919A4s in Parades over the years, in even anti-gun Maryland. It's not PC now, so they're gone. But, the law didn't preclude them.
Actually, much of this seems directed at the fact that they have such a combination, and some of are insanely jealous of it. The reasons are specious, for the most part.
Tell me. If the Police cannot own an armored vehicle, then why should you, if you want one? If the Police cannot own any Class 3 weapons, why should you be able to? Maryland's various SWAT Teams have various APC, even some with turrets. It seems that they were built that way. The US Park Police helicopter has a pintle mount for an M2. This is a Huey that their Regional SWAT uses, and it doubles as a Medi-Vac available to the public.
Somewhere along the line, it's become fashionable to complain about "excesses". These are apparently anything that they have that we want, but can't have, for reasons of local law, or expense.