Aside from the many classic reasons for deception, a 1989 study in the USA has shown that potential sex partners will lie as to whether they have AIDS or are at risk. Over 30% of the men and 10% of the women surveyed indicated that they had told a lie in order to obtain sex. When asked hypothetically whether they would lie about testing postively for the AIDS virus, 20% of the men and 4% of the women said they would.
Should people tell the truth about sex even though it will cost them immense and unforeseeable amounts of trouble? Some people claim Clinton should have said to Lewinsky: "Monica, the people need to know more about good sex. Go and tell them all the details." But that would not be the end of it. All what has come to pass would simply have come sooner.
As human beings, what we are seeking is a little satisfaction (sex) without destroying the institutional restraints that hold back chaos, which is why even the president cannot defend his actions. He can only try to minimize and apologize for them.
When you are caught having sex, it is permissible to lie. In the immortal words of Richard Pryor, the thing to say is: "Who you gonna believe, me or your lying eyes?".