There would then have been no need to include the first half of the sentence. It is there for a reason. Neither you nor I know what that reason is. That is why we have a Supreme Court to interpret laws.
Maybe someday it will be held that anyone can carry any kind of arm anywhere for any reason, but that isn’t the current interpretation. The laws of New York will probably change soon anyway, but conservatives obey the law. Part of being a conservative is believing that the United States is a nation of laws.
It's to ensure that if we the people need to band together for common defense, that we have the tools to do so.
Read Elliot's Debates of the First Congress and you won't need to rely on Ruth Bader-Ginsberg to do your thinking for you.