Kent,
I understand the point you are making with this analogy...

"A well regulated wagon train, being necessary to the migration of settlers, the right of the people to keep and train oxen shall not be infringed.

In this case, if there are no wagon trains, is the right to keep and train oxen retained? Yes. Stating one reason for a practice does not mean that the practice depends solely on that one reason."

However, the initial clause in the wording of the second amendment is there as a justification for something that many would consider a bad idea. That is, according to my reading of the 2nd amendment, I could reword it to say...

"Look, we know that having guns in the hands of the populace could lead to all sorts of mayhem, but we need a well-regulated militia to protect this new country against_____________"

Now, take away the well-regulated milita, and all you have is a bad idea that could lead to all sorts of mayhem.