If you want to argue that, say, fornication and desecration are in fact objective goods, or at least not evils, then do so. If you want to dive into ethical subjectivism and stop the discussion with a sophomoric "well, that's just what you believe" then you prove yourself unwilling to enter into argument.
Here, I'll make an argument for you to enter and to refute, if you can:
Fornication is an objective moral evil, for the following reasons:
First, it infringes upon the rights of marriage. Only spouses have the right to sex. They have this right because they have already vowed themselves to each other in a gift of self. The act of physical love is the consumation and highest expression of this full gift of self. Spouses' very body language in the conjugal act speaks marriage.
Second, fornication, no matter how well contracepted, leads to illegitimate children. These children are either killed off in the womb--another evil--or raised in domestic situations where the father is not committed to the mother--vastly inferior to married households.
Third, fornication, even contracepted fornication, is a habit of passion unguided by reason. Fornicators ignore and avoid the rational good of marriage. Though their bodies speak the language of total self-gift, they do not give themselves totally to each other by an act of willed committment. Thus they are inconsistent and irrational.
Knock my arguments down, and I'll admit my opinions are nothing more than irrational belief.