The second part isn’t a dependent clause, just as a matter of grammar. The second amendment doesn’t say: “within a well organized militia, the right to bear arms shall not be infringed.”

It’s a prefatory clause and an operative clause. The first explains the purpose, the second gives the rule. So you can certainly argue that the rule must be considered in the context of the purpose.

But that still doesn’t get you where you’re going. Because personal firearms ownership certainly facilitates raising a militia if you need one.