Low View of Marriage
In the case of sexuality, when parents have "the talk" with their children they tend to give non-biblical reasons for maintaining chastity until marriage. Rather, the reasons given for abstaining from sexual conduct revolve around fear of pregnancy/disease and/or loss of reputation. Sproul rightly points out that all of these possible consequences of the sexual act have now been aleviated by modern medical science, either through contraceptives (some of which also guard against disease) or through medical treatment. And the idea of a loss of reputation has been turned completely upside down as those who abstain are now the ones being ostracized.
This same idea extends to marriage. Since the concepts of love and marriage have been taken out of their original biblical context they have been redefined in terms of pure emotion and contractual obligations. As I'll elaborate on in my longer article, the church need not be so concerned about preventing a redefinition of marriage -- that has already taken place. The church today needs to be about recovering the definition of marriage by bringing back the biblical views of love and marriage. And this must begin in our own homes with our own children. When you have "the talk" with your kids, make sure what you say is grounded in God's word and not just selfish practical reasons! Make sure they see sex as a gift from God and that God's parameters for the exercise of that gift are set within the context of marriage. When they're ready to talk about marriage, make sure they know that this also is not only a gift from God but a sacred vow that must be taken seriously...not only after the wedding but (just as importantly) before the wedding.