Should people be allowed to take photographs in museums?

I always thought picture taking was prohibited in museums. I just spent a few days in DC going around museums and camera rudeness was rampant. People taking pictures of each other next to paintings, someone talking loudly about why her camera didn’t work, one guy monopolizing a painting by taking up close pictures of every face in it. Two questions: is it just another form of rudeness that could be allowed with some etiquette rules? And – does the need for the photo taking take away from the direct and quiet ability to experience the art? I know it interfered with my experience but am I just being an old crank?