Birth control has been a component of medical care way before Viagra, and insurance companies paid for it way before Viagra…
In addition to that, the Catholic Church is the only entity that forbids artificial birth control for the reasons it does. Even the Muslims, Jews, and non-Catholic Christians don’t have the same rules. So, I have no idea why one would expect the secular civil authorities to back it up let alone recognize it and base civil laws on it. Without the knowledge about the unitive and procreative properties that the Church requires, there is no reason to outlaw birth control yet allow Viagra. People compare the two because they don’t have the teachings of the Church on the unitive and procreative properties that the Church requires as a foundation. With knowledge of the Church’s rules in this matter, one can see that the two are completely different.
So from a secular perspective, I can see how they would require payment for both if one is covered: Both allow the sexual freedom of the patient. So speaking from a secular perspective, why should viagra be covered so that men can have sex, if women can’t have medications that will enable them to have sex (without consequences). Both are for enhancing the sexual life of those taking the medications. Because why does one use birth control? for sex without the worry of pregnancy.