and defeat the purpose of the 2nd amendment
With registration you can still have guns, so what is the purpose you refer to? The "A well regulated Militia the" part? We have a national defence agency that doesn't rely on guys with muskets any more. I don't see a no registration clause to the amendment in any event.
Actually we do rely on the "militia" for national defense. The "unorganized" component of the federal militia basically consists of all able bodied men of military age. Its something entirely different from the national guard, the federal law defining it specifically says so. You are in it by being an american citizen that meets certain criteria. The is no enlistment, no signing up, you are born (or naturalized) into it. During times of national emergency you can be transferred from the federal militia to the army or navy reserve. In other words conscripted, drafted, into the military. Such conscription is a major option for national defense.
As for "muskets". The colonial militia members sometimes had state of the art firearms for the day, better than standard issue military firearms, i.e. rifles rather than muskets. Rifles having greater range and better accuracy.
As for "well regulated", the 18th century usage of the word was referring to being equipped and practiced sufficiently to be useful. Its not referring to government imposed restrictions regarding ownership. Note that "well regulated" does not necessarily mean showing up on the town commons for drills. Owning a rifle and using it for hunting was considered sufficient, hence the "unorganized" part of the federal militia that has absolutely no obligation to enlist, show up for practice or training, etc.
Basically this topic is far more complicated than most realize.