The "abominable crime of buggery," which is not sex, was traditionally a capital crime because it is essentially the most virulent expression of hate. This explains its common connection to satanism, to suicide (Satan's final triumph), and to aggravated murder between sodomites.
St. Albert the Great gives 4 Reasons why he considers homosexual acts as the most detestable ones:
1. they are born from an ardent frenzy
2. they are disgustingly foul
3. those who become addicted to them are seldom freed from that
vice
4. they are as contagious as disease, passing quickly from one
person to another