The Instagram tag #ar15 has over 1.7 million posts, with updates by the minute  By Jon Schuppe (Repost credit NBCnews.com)UPPER MARLBORO, Md. — There are a lot of reasons people love their AR-15 semiautomatic rifles, and it doesn't much matter to them what the haters say.For some, the gun is a tool, a finely tuned machine that can cut down an animal or intruder, or pierce a distant target, with a single precise shot.For others, it is a toy, a sleek beast of black plastic and metal that de …