Ultimately it comes down to the people willing to obey or accept the rules/morals passed down. In a free society it's "the will of the people" or the given nation's citizens who effect changes in the law of their society and what is or is not acceptable.
If pre-marital sex is illegal in a country it's because the vast majority of citizens agree with the law. In the U.S. people protest to have a say in what they can do with their own bodies, who they can love, or marry. They then vote to put people in power who support their views.
Ultimately what goes on in the bedroom of two consenting adults is no one else's business. Once that is accepted as a way of life the goal then becomes to find others who share your same values.
In the U.S. we have people who don't believe in having pre-marital sex and we have those who can't imagine marrying someone they've never had sex with. To each his/her own. Instead of trying to (change) someone you simply find someone who (naturally) agrees with you.