The belief that milk is essential in the diet is clearly incorrect. You'd certainly think so listening to Lauren Bacall, Christie Brinkley and the other mustachioed celebrities paid handsomely to urge us on to ever greater heights of milk consumption. Although milk, cheese, yoghurt, butter and the like are not pivotal to our welfare, calcium certainly is. In small amounts in the bloodstream, it plays a critical part in blood clotting, muscle contraction, heartbeat maintenance, and proper nerve function. When needed, calcium is released from our bones into the blood.
Calcium is calcium, however, whether it's from broccoli or cottage cheese.
The sheer quantity of calcium in dairy products certainly makes them attractive sources, but they have no monopoly on calcium. There's no reason in the world why you couldn't get an adequate intake from a vegetable source. Anthropologists also think that until 10,000 years ago or so, all humans were lactose intolerant. The dairy industry tirelessly advances the notion that their calcium-rich foods are veritable guarantors of unbreakable bones. Problem is, there is scant support for this assertion in the medical literature.