The Constitution is widely subject to interpretation. Even though the Constitution itself is very clearly worded, even a very specific document can fall prey to the selfish (ideological or power hungry) nature of human thinking.
Leftists and collaborationists on the right (what many people call "Fudds") believes that the word "militia" means police and military. The argument falls flat on its face with the final fourteen words of the amendment ("The right of the people to keep and bear arms shall not be infringed"), but many people can fall for it.
The militia was every able bodied male and there were never restrictions on women from owning weapons. The founders wanted no standing army or federal police forces. Well regulated militia meant well trained militia.