I don't think I have ever heard of a user of a full-auto M-14 say that is was worth using in that mode as anything other than an area denial weapon.
Tough to control and aim accurately, and the Army tried all sorts of devices and tweaks to make full-auto fire out of the M1A a useful option.
There were some promising results with a very highly modified M-14 in full-auto fire, but the developments came too late, and the project was shelved. it is most unlikely your Dep't would shell out the considerable money needed to replicate the above variant.
In view of the standard M-14's inherent tendency to put bullets in unwanted directions when fired by the typical user when in full-auto mode, and the attendant liability when used so in a civilian environment, leave the happy switch as it is.
The Mil put the lock on there for good reasons.