The cans aren't hard to warm up. A hexamine tablet (or two or three, depending on the size of the can) will do it, as will a sterno heater. Both the stew and pork and beans can be eaten cold, I've done it with C-rations many times. (I refuse to eat canned spaghetti cold. Or warm, if I can help it.)

A squad on patrol is not going to lug around a Big Berkey. But a family can include it in their 72-hour bags, because mine does. If you're tactical, you carry your water. But if you carry MRE's because you're tactical, you have to carry that much more water. You really don't save anything in weight.

True, the MRE's are more convenient. But you're paying a pretty hefty price for that convenience, and I'd rather spend that money elsewhere.

Onward and upward,
airforce