I wouldn't want to either.
I think their relative scarcity in the US is due more to the impracticality of owning them rather than any legal strictures.
If gang-bangers wanted to use full-auto on a regular basis, they would.
But I can think of only one crime in the past decade or so that involved a full-auto.
The scarcity is due to limited supply and the resultant high expense - there are only a finite number of legal Class III/ full auto receivers available, and recent manufacture machine guns are not legal for non-governmental entities to own, period.
If new receivers were legal, you would see a volcano of full auto enthusiasm erupt. Right now, it's just the same old tired guns being passed around - as they wear out and disintegrate, no more will be available.
That's the NFA/ full auto dirty little secret.
I own and shoot several: AR-10, AR-15 w/ silencer and 1928 Thompson .45cal. Nothing *impractical* about 3-round burst or full-auto, IMO. Please explain how impracticality is related to scarcity.
And to cover the sniper rifle angle, I have a Barrett M82A1 .50cal BMG on order, and am breathlessly awaiting delivery in October. Talk about impractical...