The whole point of insurance is to pool risk. Many insureds are riskier than others for one reason or another, often because of their personal behavioral choices. Under the logic of these posts, people who ride motorcycles should not be insured for their injuries, and people who eat themselves into diabetes should not be able to access insurance for their care. Which may well be the desired outcome for these two posters. If so, they should just say they're against all insurance and want everyone to pay for their own health problems out of their own resources, or die if they're unable to do so. If we're going to have insurance, there is no reason that insurance should not cover against the risk of pregnancy (or endometriosis, or menstrual pain) in the same way that it covers the risk of motorcycle injuries or gluttony-induced diabetes.
Limiting this argument solely to female sexual behavior and reproductive health doesn't make any logical sense. When people attempt to make this argument, most rational observers will conclude that the proponent either has not thought their position through or that the proponent is a sexist ass.