In fact, you can not be a true Christian and stand idle or condone those who are practicing homosexuals or those who engage in any sexual relation outside the bonds of marriage.
Paul, in the book of Romans, instructs Christians to not condone or approve of those involved in any sinful practice, including homosexuality. In Romans 1:26-27 Paul exposes those who are homosexuals - both men and women - as engaging in unnatural relations, the result of "shameful lusts." In verses 28-31 he goes as far as to group homosexuals with a bevy of other wicked and evil sins such as deceit, murder, gossip, slander, God-haters, arrogance, and even those who simply disobey their parents to name but a few.
For faithful Christians though God has given warning concerning condoning or tolerating sinful acts. Romans 1:32 explains that they know what God has said concerning those sins and that simply approving of those who do them are worthy of death. The verse is principally speaking to those who are engaged in those sins, and by extrapolation it is applied to those who are faithful Christians as well.
But this story doesn't end there. God is about love. The theme of the Bible is love. In fact Mark 12:30-31 puts it very plainly:
 "Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.  The second is this: ‘Love your neighbor as yourself. There is no commandment greater than these.”So while we are not to condone the sinful actions of others, we ARE to love all mankind - even our enemies and those that persecute us (Matthew 5:43).
Remember, none of us are perfect for ALL have sinned (Romans 3:23) and while we are not to condone the sins of others we ourselves must always look to correct our own sins too (Luke 6:42).