One of the more controversial of Catholic teachings today is its claim that homosexuality is an objective disorder. Many people argue that because homosexuality is not chosen (which seems to be the case, whether or not its origins are genetic, psychological, or a combination of the two), it's demeaning to claim that it's a disorder.
To better understand the theological underpinnings of this teaching, I'd recommend Msgr. Livio Melina's article, Homosexual Inclination as an "Objective Disorder": Reflections of Theological Anthropology. Be attentive and patient in your reading... it's weighty, but well worth it.
[Thanks for Fr. Bryce for the link.]