infabilly:
So there are passages in the bible condeming homosexuality and premarital sex, as we all know.
However there are also passages in the bible that suggest it would be quite alright for a father to sell his daughter.
But even so… why do we choose these things to be such huge sins these days?
What about the 10 Commandments? The 7 Deadly Sins?
People break them every day without any notice.

It helps to know the context. It also helps to understand that people’s understanding of revelation develops—in a sense, God has had to put training wheels on our tricycles, because it takes us a while to grasp things. I say this because, in the case you mention, I believe that selling the daughter was an advancement on the practice of the day, which was killing (I could be misremembering, so perhaps someone else can confirm this).
Also, you need to distinguish between the Ten Commandments ,which largely reflect natural law, and the various Old Testament rules of practice which may not. Example: it is “written in our hearts” (natural law), that murder is wrong. It is not “written in our hearts” that a particular practice might involve selling one’s daughter.
The 7 Deadly Sins seems to me to simply be a list of those grave sins that we are inclined to and should be avoided, as they lead to a severing or a weakening of our connection with God. As such, I always view them as warning signs, so to speak: watch out for these! They aren’t “commandments”, and so we really don’t “break” them—we commit them.
As for people breaking them every day without notice: God notices, even if modern man has decided that God doesn’t exist. Some people have lost the sense that there is a hell----all they have to do is be “nice”, not hurt anyone, and—whoosh!–=it’s off to heaven when they die. This simply reflects the relativism that has permeatd society. It’s easy, too----it’s far easier to say that one is “not religious but spiritual”, and go on one’s way, because that person’s God never asks anything of them, and their God always approves of everything they do. The road to hell is very broad…