I think seriel sex before marraige is wrong. Sex is like velcro, it's the glue that really cements a special relationship. The biggest problem is that it complicates the relationship, making it harder to let go and break up. Then, the next time you have sex in a new relationship....it isn't as special as the first (or previous) relationships. The "bond" of the Velcro loses it's stregnth. Plus, when you are finally with your soul mate, you feel "silly" when you think of your past "loves."
Call me old fashioned, but I see value in not "giving it freely" away.
But, I also see alot of terrible marraiges within the JWs, all caused by the "no sex" (including masterbation) before marraige and pent up frustration