The calendars are essentially packets of posters, so yeah, part of the point is to rip the pages out. I've even seen individual calendar pages for sale as posters. Really though, since they put the days in lines rather than in a block, their utility as a calendar is pretty limited. It's not like you're going to throw away the pages afterward, right?
I personally tried to use a sharp knife to do it more cleanly, but yeah, it's something of a pain to do. Though it is possible to rip cleanly along the metal clip, it definitely would have been better to do a perforation on each sheet. But eh, 7 posters for one price is pretty good in my book, even if you have to do some of the work yourself.