I don’t understand why you are attempting to equate malfunctions of the body with fertility. Certainly, a runny nose or a sore throat are “natural” responses to many viral and/or bacterial infections, but simply because they are “natural responses”, they are more accurately described as “natural defenses”. “defenses” against the infection.
Fertility, and the “natural responses” to it are not “natural defenses” against anything. So to equate taking a birth control pill to control one’s fertility with taking an aspirin to control a runny nose seems to be a flawed analogy. The two biological processes are inherently different; the fact that they are both “natural” is irrelevant. Again, one is a natural defense, the other is not.
Even setting aside that problem, you completely fail to address the artificial sweetener example. Fat is certainly a "natural response" to calorie consumption, but even your convoluted argument has no way of redefining it as a "natural defense" against anything.