Whats wrong with contraception? As long as it's purely contaception and non abortifacient then it's not taking a human life. Are your objections to it the "spilling seed" argument or the "be fruitful and multiply" argument?
Contraception is wrong on many levels, my friend. The relationship of Adam and Eve before the fall should be seen as our model b/c it shows us how God intended man and woman to interact. There, we see that man and woman are to be "one flesh" and they are to "be fruitful and multiply."
The idea of two becoming one envisions a total and complete giving of oneself to the other. Two can become one only when there are no barriers between them and no witholding anything from the other. The seed of man and the womb of woman are precious because it is by these that man is able to participate in the work of the Creator. By these God brings his greatest work of art into the world: a human being, who bears the very image of God Almighty.
But then we come along with our condoms, creams, birth control pills, and RU-486 clouding the vision that God had in mind for his people. Now two become about a half, with only partial self-giving and always holding a little something back. It's as if we say to Him, "I don't care that you have made me to participate in your work. I want it my way." It's as if we say to each other, "I don't love you enough to share with you my procreative power."
Besides Adam and Eve in the garden, we can also look to the design with which we were created. Look at the human body and the functions that each part is intended to play. Look at how human beings are supposed to be created. God gave us our "private parts" for a reason, and intended a particular use for them. Whenever we use our bodies for something other than what God made it for, we sin.
To put it another way, the use of contraception is a violation of the natural law of our bodies. Our human sexuality is supposed to be unitive and procreative. Contraception denies both of these ends. Thus, it is a grave sin.
Finally, I have never seen any proof from Scripture that contraception is morally acceptible. I've only seen passages that speak against it, the sin of Onan being only one. There are many others (here). For more on the immorality of contraception, go here for a list of 37 articles on the subject. You can also read about Natural Family Planning here.