I guess I would point to several things mix:
Genesis 1:27-28 - This is really God's first commandment - Be fruitful and multiply. He puts no qualifiers on it - aka it doesnt just apply to Adam and Eve or to get the population going.
Sex is by it's very nature procreative and unitive. When you try and separate these, you try and separate things the way God created them. He did this for a reason, that that which unites a husband and wife in marriage would also be that which brings forth fruit, and love. Also, it is pleasurable for a reason. Also, the procreative nature is what separates sex between a man and a woman from homosexual sex or even bestiality, which are condemned in the bible.
Ps 127:3-5 - children are a gift from God
Hos 9:10-17, Ex 23:25-26, Dt 7:13-14 - these basically outline barreness as a curse, not something wished upon one's self, etc
In the NT, Christ cursed the fruitless fig tree
In the end, I would have to say that the vows that are taken at the altar is what is being expressed in sex. Sex is, essentially, the marriage vows become flesh. When you profess vows on an altar, they involve 4 main things- a giving of the self totally, faithfully, freely, and fruitfully. If you dont plan on having kids, you are withholding your fertility, you arent giving yourself freely because you are putting conditions upon it, you are therefore not giving yourself totally, and you arent trusting that God knows best.
Contraception and abortion were not created to prevent children. Abstinance already worked for that (and if you have no self control, well, then you arent giving yourself freely because your "Yes" only means "Yes" if you can say "No."). Contraception was created so people could separate the life giving aspect of sex from its unitive/pleasurable aspect. Back in the times of ancient Egypt, they used things such as animal intestines stuffed inside the woman. During the Renaissance, wooden blocks (I guess you could call it an early form of the Diaphram) were placed in women. In China, women used to actually drink Mercury to make themselves infertile (and yes, you can die from Mercury consumption). In fact, every single Christian denomination condemned contraceptives up until the 1920's when the Anglican Church approved it's use in limited cases, opening the door a little. It is, as you probably know, wide open right now.
What is wrong with present day contraceptives and birth controls? Well, medically speaking, the hormonal ones such as Norplant and DepoProvera actually increase a woman's risk for breast cancer among other things. There are also some women who have been rendered infertile as a result of these, and others who have miscarriages after going off as a result.
It also promotes premarital and extramarital sex. There are no strings attached if there are no kids. It is a general denial of any responsibility for the action taken, aka sex.
Onan in Genesis 38 used an early form of contraception - withdrawl. He was struck down for this.
The use of contraception or the general denial of children is one of the main things supported by American society. The body has gone from the temple of the Holy Spirit to something that we are ashamed of, to something that we hide, and to something that we can no longer freely give of. Marriage and love DEMAND a total gift of the self. When Christ was on the cross, this is EXACTLY what HE did - He gave of Himself TOTALLY. When we withhold part of ourself from our bride we are desecrating the very vows that we take at the altar, and lying with our bodies. Sex as God created it demands a total gift of the self. Sex straying from that, with the use of contraception or whatever, is a flat out lie.
Romans 1:24-25 - Therefore, God handed them over to impurity through the lusts of their hearts for the mutual degredation of their bodies. They exchanged teh truth of God for a lie and revered and worshiped the creature rather than the creator, who is blessed forever.
Sex with contraception denies the Creator. It says "I know what is best for us." It says "We dont want you involved in our one-flesh union in the most intimate ways." It says, "We dont want the gift of children that you give us." Some say that if God wants them to get pregant, contraception or not, He will. This leads to unwanted children (deny it if you will, but if you are using contraception, you dont want kids). So then why even be on contraception? Are you worried about your financial state? There are ways that you can continue without using contraception and without denying God that are wholesome and actually strengthen a marriage.
If you want me to say more, I can.
The bottom line - contraception and abortion are just a few of the many manifestations of the attack on sexuality, which also include lust, sexual abuse, pornogrpahy, adultery, divorce, self-hatred, test tube babies, rape, homosexuality, transvestites, plastic surgery, transexuals, sexual obsession, prostitution, pedaphilia....and the list goes on. This is a HUGE attack by Satan?
Why - We are created in the image and likeness of God. He stamped our very call to love into our bodies. The first effect of the fall was that Adam and Eve felt shame and they covered up. The desanctification of sex and marriage and of the human body are HUGE because they point us to Christ. Our very bodies help us to discover our life's call. And yet we have to cover them up. Hated is not the opposite of love, but lust. Lust is like darkness - instead of an absense of light, it is an absense of love. This world is so twisted. Playboy is a $10 billion a year business. Playboy has 3.5 million subscribers, and 20 million porn magazines are sold each month. Playboy's website which has some free teaser shots gets 5 million hits per day. THIS IS HUGE! These are just a small sampling of a nation which is buying into Satan's lies, into the objectification of mainly women, but some men as well. What a tragedy it is that such beauty is being sold to the lusts of men. Things are so bad that we can't even have crosses with Christ as He was truly crucified - naked - AND WITHOUT SHAME (reference to Adam and Eve's shame). He came to set us free from the bonds of Satan. Look around you. They are everywhere. And they are heavily ladden upon sexuality.
God bless