Careful... You are starting to use the same line of reasoning the gun-grabbers use when they want to take my AR-15 away. Why allow ownership of a semi-automatic baby-killing assualt rifle with 30-round magazines when nobody really needs one.
Of course, I do understand that one is protected by The Constitution while the other is not. But in the end it comes down to freedom. Prior restraint is generally a no-no in a free country. Punish speeding but don't outlaw cars capable of speeding. There are lots of dual-use items that could be outlawed if we start down that slippery slope.
A car is a very public item while a gun is not. You wouldn't permit an 18 year old to set up a gun range on a busy street but we do allow him to get behind the wheel of a 500 HP 3000 pound car on that same street.