Women should not give out sex until a man demonstrates that he is interested in a commitment- that is, unless the woman wants a shallow, meaningless, short relationship.
Men do not marry women they don't respect- and a woman who sleeps with a man right away with no love present or expectation of commitment is not respected.
Second class behavior.
The best wait until marriage.
After all, a man should not trust a woman as much who holds to a lesser standard.
To hold to a lesser standard, is to say she is more likely to some day again find a convenient excuse for bedding someone she is not married to--but this time someone other than her husband.
One should understand, however, that the majority of men do not understand this themselves--but rather they are endowed by evolution with certain emotional guides that tend them in varying degrees, to such judgment (such emotions are often consciously rationalized as "respect").
I would never marry a woman who had sex with me before marriage.
But I would have sex with her.