Gorgias:
Sex is not intrinsically evil; there are licit circumstances in which sex is good.
precisely, my question is though, are all these circumstances only within the marriage bond?
Yes.
what is it about a wedding ceremony that magically makes sex licit?
Magic… LOL!
It’s the fact that a wedding ceremony is a
covenant, in which you promise, to your spouse and in front of God and the community, that you make a life-long commitment to your spouse. It’s the fact that Jesus made marriage a sacrament, and by virtue of the wedding ceremony, you’re participating in that sacrament. It’s the fact that the liceity of sex proceeds from your explicitly expressed, legally binding, and sacramentally blessed commitment to the relationship “until death do you part”. No magic… just
sacrament, though!
if two unmarried people with a strong emotional bond wish to have a deeper physical relationship, what is mortally sinful about that?
It’s that they’re taking actions that are only valid in the context of the sacrament of marriage (since physical intimacy is meant to strengthen that sacramental bond and make that life-long bond physically visible in the very lives of their children), and are ‘stealing’ them for themselves outside the sacrament. In a way, it’s analogous to an atheist taking Communion – he has no intent to participate in the spiritual and sacramental reality of the Eucharist, but is just taking the physical part (the bread and wine) on its own merits. It’s a denial of the reality of the sacrament of marriage.
if they practice NFP then their procreation would also be unitive and procreative.
It would be open to procreation, true, but what would that procreation be a sign of? It’s meant to be a sign of their life-long commitment to one another. (After all, what’s more appropriately a sign of life-long commitment than parenthood?) But, there’s no (sacramental) commitment there, for it to be a sign of! So, in a very real way, procreation outside of marriage is a
lie.
And, it wouldn’t be unitive, either. What bond – what sacramental commitment – would it be uniting? None. So, although it might deepen their relationship, it wouldn’t be
unitive – it would just be “fun”. It would be “loving”, but in a superficial and dishonest way: “Honey, I love you so much that I want to share my entire body with you. Umm… well, I don’t love you so much that I want to commit my entire life to you… but maybe we could pretend for a bit so that it makes me feel good for a little while…!”
we are born innocent but throughout our lives we give in to temptations and become selfish.
Well, let’s be clear here: it’s not that I’m saying that fornication
doesn’t lead you to greater sin – it does! However, it doesn’t occur without having been led to the brink already. So, I’m willing to amend my argument, based on your assertions. Yes, fornication leads to (greater) selfishness. However, it’s a sign that selfishness already exists in the person. (In other words, you’re selfishly taking, for your own personal benefit, something that belongs only within the state of marriage. You’re taking it from yourself (and diluting your potential future experience of it), and you’re taking it from your partner, who should only be offering it in the context of marriage. Whether or not it’s freely given, it’s still sinful – it’s a gift that cannot truly be given outside of marriage, so even if both of you assent, you’re still ‘stealing’ from one another.)
fuurthermore if you were correct and fornication would be a mere symptom, then why would it be a mortal sin? then we should determine what is causing our selfishness and address that, wouldnt you agree?
You’re correct, in that in the case of
any mortal sin, we need to see what’s causing us to separate ourselves from God and address that shortcoming. The fact that a person has a symptom doesn’t mean that they don’t suffer from the disease!
what makes fornication sinful is the same thing that makes eating sinful. if you over-indulge, and if you get to the point where you are willing to sacrifice other people’s health and well-being to get your pleasure then its a mortal sin. this is true with sex, food, wine, wealth, etc. but if you are able to obtain your pleasure without it harming others, and if you dont treat it as the most important thing in your life, then how is it sinful?
A-ha! That’s exactly the point! Fornication
cannot exist without harming others! It damages your outlook, and your partner’s, and anyone you come in contact with who thinks to themselves, “well, I guess it’s ok – after all, someperson555 seems to be a nice guy, and look, he’s doing it!”.
The perspective that “it doesn’t hurt anyone” is exactly the rationalization of the sin itself!
simply expreriencing pleasure cannot be what is sinful. therefore its logical to conclude that the sin lies in the effect it has on the individual.
There’s some truth to that; sin exists in the effects that it produces; however, it doesn’t exist
exclusively in the effects. For example, suppose I experienced pleasure by stealing your car and driving it. Wouldn’t the experience of that pleasure be tied up in the sinfulness of the act?

(Yes, there’d be sinfulness in the effect it has on me down the line, but that wouldn’t be the only place where the sinfulness would lie!)