"Reason attests that there are objects of the human act which are by their nature "incapable of being ordered" to God, because they radically contradict the good of the person made in his image. These are the acts which, in the Church's moral tradition, have been termed "intrinsically evil" (intrinsece malum): they are such always and per se, in other words, on account of their very object, and quite apart from the ulterior intentions of the one acting and the circumstances." (Veritatis Splendor, n. 80 St. John Paul II)
"Neither is it valid to argue, as a justification for sexual intercourse which is deliberately contraceptive, that a lesser evil is to be preferred to a greater one, or that such intercourse would merge with procreative acts of past and future to form a single entity, and so be qualified by exactly the same moral goodness as these. Though it is true that sometimes it is lawful to tolerate a lesser moral evil in order to avoid a greater evil or in order to promote a greater good," it is never lawful, even for the gravest reasons, to do evil that good may come of it -- in other words, to intend directly something which of its very nature contradicts the moral order, and which must therefore be judged unworthy of man, even though the intention is to protect or promote the welfare of an individual, of a family or of society in general. Consequently, it is a serious error to think that a whole married life of otherwise normal relations can justify sexual intercourse which is deliberately contraceptive and so intrinsically wrong." (Humanae Vitae, n. 14 Blessed Paul VI)
Q. 929. What is the scripture proof of this?
A. Out of Gen. xix. 13. where we read of the Sodomites, and their sin. “We will destroy this place because the cry of them hath increased before our Lord, who hath sent us to destroy them,” (and they were burnt with fire from heaven.)
from the CCC:
1867 The catechetical tradition also recalls that there are “sins that cry to heaven”: the blood of Abel, the sin of the Sodomites, the cry of the people oppressed in Egypt, the cry of the foreigner, the widow, and the orphan, injustice to the wage earner.
I am going to print these words while I have the chance.
Sodomy is a serious sin, which cries out to God for vengeance.
Fornication is always, always wrong.
"A morally good act requires the goodness of the object, of the end, and of the circumstances together. An evil end corrupts the action, even if the object is good in itself (such as praying and fasting "in order to be seen by men"). The object of the choice can by itself vitiate an act in its entirety. There are some concrete acts - such as fornication - that it is always wrong to choose, because choosing them entails a disorder of the will, that is, a moral evil." (CCC, n. 1755).