I do agree in many ways, however, it is worth noting that the reproductive mechanics are very different between cats and dogs.
Queens (female cats) are induced ovulators, meaning they do not ovulate until they are stimulated by the spines on the tom's penis during mating. Cats will cycle pretty much constantly unless and until they are bred or spayed.
Bitches on the other hand cycle on a fairly predictable basis, however, the reproductive cycle in the bitch is driven by progesterone.
Progesterone is an inflammatory hormone that causes, among many other things, the congestion and thickening of the uterine lining. The bitch is UNIQUE among mammals in having this reproductive cycle that is driven not by estrogen, but by progesterone.
The inflammation of the uterine lining is what takes each bitch one step closer to a pyometra each season she goes through. Some bitches may tolerate this uterine inflammation during the reproductive cycle and never develop a pyo. Others take many less cycles for them to develop to the metritis/pyometra stage.
Dr. Hutchinson is very specific about this in his seminars and online information.
Pyometra is in general an emergency situation for any bitch, and requires aggressive treatment in order for a bitch to survive.
So I would agree that leaving open bitches to cycle for long periods of time without either breeding, or ovariohysterectomy, is not healthy for the bitch, and unwise. This should not, however, be used as a justification to breed a bitch endlessly because it's "unhealthy" for her to stay open.
JMO as always.