Just because taking a gun on a plane would be technically legal in a Ron Paul administration doesn't mean the airlines themselves would allow passengers to have one.
The airlines have the final say because the plane is their property.
It does likely mean that airline security and pilots would be armed though.
Yea this is the key. The point here isn't just about stopping terrorists hellbent on taking over a plane. It's also about the property rights of the airlines. Just as Virginia Tech had the choice of whether or not allow guns on campus, airlines should have the same choice.
Airlines would be free to impose their own rules. If they allow passengers to carry guns, and that makes you feel unsafe, then you will fly another airline. That's how the free market determines these things.
Right now, the federal government has tyrannical control on airline security. As most of us here believe, the government can accomplish very little through rules and regulations that the free market cannot do faster, cheaper, and safer w/o on its own.