The spirit indeed is willing, but the flesh is weak.
Matthew 26:41 (KJV)
So how have some these priests endured sexual desires? Many would say having sexual acts with younger children if not with other men (homosexual and/or bisexual) and/or women too (heterosexual only).
The best option is for the clergy to marry. This way the sexual animal is satisfied and the Christian person may worship God in word and deed.
Vatican hit by gay sex scandal
Vatican chorister sacked for allegedly procuring male prostitutes for papal gentleman-in-waiting
http://www.guardian.co.uk/world/2010/mar/04/vatican-gay-sex-scandal
Pope defiant over child sex abuse
Senior Catholics across Europe use Easter addresses to apologise and acknowledge the damage caused by the scandal, while pontiff remains unrepentant
http://www.guardian.co.uk/world/2010/apr/04/pope-defiant-child-sex-abuse
Anyway you see it, sexual abuse of younger children is horrible crime. In my opinion, a man who abuses a child should be castrated. Unfortunately what triggers sexual abuse is not the penis and/or testicles, but rather the mind. Hence the best option is to kill the abuser. The latter is not a Christian thing to say, but sometimes you need to cleanse humanity from its filth whether he wears a robe or not.