Well, you are focusing on the prefatory clause:
A well regulated Militia, being necessary to the security of a free State
While pro-gun advocates will focus on the operative:
the right of the people to keep and bear Arms, shall not be infringed
But since you brought up the word militia, let's see how the constitution defines it in Title 10, 311:
The militia of the United States consists of all able-bodied males at least 17 years of age and, except as provided in section 313 of title 32, under 45 years of age who are, or who have made a declaration of intention to become, citizens of the United States and of female citizens of the United States who are members of the National Guard.
Which includes the National Guard and "Naval Militia" and...
the unorganized militia, which consists of the members of the militia who are not members of the National Guard or the Naval Militia.
In reality it appears that different founding fathers had different intentions when the document was being created. For example, Elbridge Gerry feared that Congress may not actually arm "the militia" so his intentions probably were to make sure citizens had the ability to remain armed. You might not agree with that deduction, but maybe you can at least agree that the 2nd amendment's position in the Bill of Rights is an important one.
Jefferson, who didn't really have a direct hand in the 2A, said:
""Laws that forbid the carrying of arms ... only disarm those who are neither inclined nor determined to commit crimes. Such laws make things worse for the assaulted and better for the assailants; they serve rather to encourage than prevent homicides, for an unarmed man may be attacked with greater confidence than an armed one."
Of course, Jefferson said a lot of things that we would consider radical today. I'm merely demonstrating that there is no unified intention among the framers.
Personally, I think the 2nd amendment was created to protect the free citizens of the US. From foreign threats and domestic alike. Whether you think either is likely or relevant today is up to your own world view.