One things Christians are often accused of is intolerance. Though there are some intolerant people who claim to be Christians, most Christians are not intolerant. The basic problem lies in what the world has begun teaching as the definition of tolerance.
"Intolerant" means "unwilling to grant equal freedom of expression especially in religious matters" or "unwilling to grant or share social, political, or professional rights" (Merriam-Webster). So when you see somebody proposing legislation that restricts what pastors can say from the pulpit (e.g., ENDA), or regulations that prohibit students bringing Bibles to school or wearing faith-based T-shirts, you are seeing intolerant behavior.
Why, then, do we keep hearing that saying "homosexual behavior is sinful" or "promiscuity is a sin" is a form of intolerance? It is because they are trying to convince us to become indulgent. "Indulge" means "to treat with excessive leniency, generosity, or consideration" (Merriam-Webster), with the key word here being "excessive". Another word that describes how the world wants us to walk is "licentious" ("lacking legal or moral restraints ; especially: disregarding sexual restraints" or "marked by disregard for strict rules of correctness", Merriam-Webster).
Without delving into Scripture, we know that sexually promiscuous behavior leads to depression, diseases, and unplanned pregnancies. Paul warns us in his epistle to the church in Galatia against "sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these" (Galatians 5:19b-21a, ESV). I will not take up too much space here by giving a laundry list of how each of these things is bad in a strictly secular sense, but I'm sure you can imagine on your own. Do you think it is "intolerant" to warn other people that these types of behaviors are dangerous?
Remember, intolerance tries to keep you from expressing your faith and warning others about the wages of sin (Romans 6:23). Just be nice about it and let them know about the free gift, too.