We are made in the image and likeness of God. In His image, we are spiritual. In His likeness, we are able to create, in cooperation with God, new life – we are “like” Him. The devil cannot create life. To render ourselves incapable – even temporarily – of creating life, we take on the likeness of the devil and forsake our “likeness” of God. So, yes, contraception is in opposition to God’s will, ergo, sinful.
BK
The Catholic Me 