You seem to be laboring with a misconception. contraception and abortion are not the same thing;
Contraception loosely defined is the prevention of a pregnancy, while Abortion is the termination of a pregnancy. And while there is some merit to your saying that they both thwart God's plans, you must balance that with the fact that an omniscient God knew that those choices would be made before he created the heavens and the Earth, and also it must be balanced with God not interfering with man's free will.
As far as to the prevention of life, yes it not only prevents one life, but also the lives of their posterity, which is a direct disobedience of God's command in:
Genesis 1:28 And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth.
From this we see that God had a secondary purpose in creating man which was to have him care for the rest of God' creation, and by putting man into the Garden of Eden;
Genesis 2:15 And the LORD God took the man, and put him into the garden of Eden to dress it and to keep it.
And even though man seems to be in opposition to God's will at almost every turn the truth is that:
God is all about forgiveness!
Psalm 103:10 through 12 He hath not dealt with us after our sins; nor rewarded us according to our iniquities. For as the heaven is high above the earth, so great is his mercy toward them that fear him. As far as the east is from the west, so far hath he removed our transgressions from us.
God is never so far away that he cannot hear our prayers of contrition.