I agree you can get in shape without weights but its still not the most effective method for gaining muscle. You'll quickly hit a wall for how strong you can get without the use of weights. Doing more of a lesser weight, e.g. your bodyweight, is not as effective at building muscle as doing less reps with a higher weight.

and crunches are pointless... unless you enjoy straining your back and neck. I used to do them all the time until I realized i could get a flat stomach through running and diet, without ever doing a single crunch.