Human beings, on this view of things, have an enormous responsibility on their shoulders: to make themselves either into something beautiful, something resembling God, or else into something hideous and demonic. So there can be no lax and loose attitude about life. On the contrary, life is serious business, because of the deep mystery of human freedom.
So much in our day and age runs contrary to this. Many people—myself included, in many ways—try to live their lives in ways that avoid responsibility and consequences. This is especially true as regards sexual ethics. People try to have sex casually, enjoying themselves without committing to a lifelong relationship or to having and raising children. Or if keeping a child is inconvenient or difficult, the child may be aborted so that the consequences of the sexual act can be neutralized.
But God has not made us to live our lives this way. The natural consequence of sexual intercourse is procreation and the emotional union of the two parties. They care for each other and for the child they bring into the world. They are vulnerable and depend on one another, so they have to commit to being there for one another. But all this means assuming profound responsibility, and taking one's actions with the utmost seriousness.
A sinful, vicious life is a life that attempts to avoid commitments and responsibility. It's lazy, it's casual, it's unforgiving, it is not sacrificing, it is not deeply loving, it's not concerned to help others. Not all of us live like this in any extreme way. But the seeds of such a vicious life are planted every time we act in a way that avoids responsibility and commitment in pursuit of instant gratification, and if we water these seeds through continued action in the same vein, before long these seeds will grow into a hideous thicket from which the is no easy escape.