Have you heard of the natural law? It is an rational ethical system based on the "ends" or purposes of human nature. We are against any government that rejects the natural law, as the natural law can be known by human reason alone, so any rational person should accept it. It is one thing for the secular state to reject religious law; it is another for the secular state, which glorifies reason, to reject the natural law which can be known through reason.
Following Scripture and the Church Fathers, as well as the Natural law, Catholics understand sex as being for the purpose of procreation. In fact, the denial of procreation, either as itself (contraception, sodomy, masturbation, etc.) or its effects (a child that needs a family to raise him, which divorce frustrates) are the cause of all merely sexual perversion.
Notice, from the Catholic point of view, that if you accept contraception, we deny that you can argue against sodomy. If you don't think sex is for procreation, which approval of contraception requires, then you can't denounce sodomy either, except of course by appealing to Divine Command. We actually agree with the author of the second article that, given marriage is not about procreation, it follows that there is no reason to reject gay "marriage." However, we Catholics simply deny the premise "Marriage is not primarily about procreation." To put it another way, we think that the acceptance of contraception (which all Christians, Protestants and Catholic, didn't accept until the early 1900's) led to the acceptance of sodomy.
Anyway, one might notice that rape is not really against procreation in itself. I wish to clarify that the evil in rape is not in the sex act, but rather because the sex act happened without consent. As such, this makes rape far more evil then any of the sins above, because instead of it being a sin against sex, it is a sin against justice.
Modern sexual ethics, on the other hand, don't accept that sex has any inherent purpose, but rather a purpose as we define it. In other words, sex can be for procreation, but only if we choose for it to be so. From this principle, no sex act alone can be wicked; only sex without consent can be wicked, as rape is not evil because of the sex act, but rather because of non-consent. This is why I mentioned above how rape is not a problem of procreation, but a problem of consent- and justice.
In fact, the entire principle of the Sexual Revolution is that, in the words of Philosopher Peter Singer "sex brings up no serious moral questions." Any sex act*, under this view, is good, as long as it is consent among all persons involved.
*Pedophilia is wrong, in the Sexual Revolutionist's eyes, because a child is not mature enough to consent.