This is why Christians have become increasingly more OK with contraception and gay marriage -- because the Bible has never explicitly said "thou shalt not marry of the same sex" nor does it say "thou shalt not contracept." Instead, we have verses that back up the principle of each of these things.
We know that marriage between two people of the same gender is wrong because we know what marriage literally is and its criteria. Plenty of Christians use Scripture to try and support gay marriage by showing that the Bible doesn't talk directly to it; for instance, many Christians (including one of my sisters actually) believe that Sodom and Gomorrah's sin had nothing to do with homosexuality, but about abuse and not being hospitable. Many twist verses like Leviticus 20:13 as talking about lust, but not homosexuality itself.
Of course I disagree with them because we do know that acting upon homosexuality, even if the couple tries to approach it as Christian as they possibly can, it still acts outside of God's framework and criteria.
Likewise, I view contraception as almost the straight man's version of this. It is much easier to suggest it is OK because 1) it is convenient, 2) the Bible doesn't make explicitly direct statements on contraception, and 3) it's convenient.
But like gay marriage, contraception acts outside of God's framework and criteria of marriage. Sex is meant to be the holy vocation put into the form of flesh where the two become one, and each giving of themselves entirely. Contraception restricts part of the giving process and interjects what God intended.