THE CHRISTIAN GNOSTICS (over the years)
If Jesus so adamantly opposed promiscuous sex, as is said today, then why did many early Christian sects exist that ritually practiced open-sex? I mean, when one deviates from something they agree to obey, they usually don’t go the total opposite. Logic dictates that Christians who opposed promiscuous / free sex did so because of the strong secular persecutions against it.
Eerdmans Handbook to the Bible, 1983, p. 498, “The Religious Background of the New Testament”:

The Body and Society: Men, Women, and Sexual Renunciation in Early Christianity, Peter Brown, 1988, “’A Promiscuous Brotherhood and Sisterhood’: Men and Women in The Early Churches,” p. 147:

The Encyclopedia of Religion, Eliade, 1987, vol. ?, p. 566, “GNOSTICISM”:

http://members.iinet.net.au/~quentinj/Christianity/Gospel-Timeline.html, The History of the Gospels – a Chronology: A summary of the evidence of the Gospel formation (4-2-02):
The earliest Christians are the Gnostics
…
“Early Second Century (100CE -149 CE)”:
The Gnostics are dominant and vital figures and teachers in this period and are the mature flowering of the the great creative urge welling up in this period in Christianity and other movements.
http://www.featherlessbiped.com/6696/satan.htm, Satan: Prince of the World, by: Gene Taylor, Anderson County Sheriff's Office, "Gnosticism":
Early Gnostic rituals share elements with the satanic mass, namely a secret feast, a sexual orgy, reversals of the Christian mass, ritual use of blood, semen, and other excretions, and the practice of infant sacrifice and cannibalism (Katchen, 1992).
The Catacombs of St. Callixtus, St. Sebastian, and Domitilla, Englefield, 1913, p. 64, “Glossary of Words, etc. in connection with the Catacombs | Gnostic”:

http://homepage.mac.com/shanerosenthal/reformationink/srirenaeus.htm, Irenaeus and A Multitude of Gnostics:
Gnostic Ethics
When it comes to Gnostic ethics however, more varied approaches are evidenced.
For example sects such as the Saturnites and Encratites were very ascetic and
legalistic in their lifestyles, whereas the Carpocratians,
Nicolaitans, and the Ophites were antinomian, and indulged in sensual pleasures
and licentiousness.
http://www.gnosis.org/thomasbook/ch4.html, Beyond the Law: The Gnostic Apostle Thomas: Chapter 4, “Pearls in the Mud”:
Gnostic responses to the problem of sexuality tended to be extreme: complete abstinence, or complete license. Extreme austerity -- encratism -- was the more usual solution, at least in principle. For some sects, however, free indulgence of the sexual urge was not only permitted but commended.
“Complete abstinence, or complete license”: simply because the principle teaching of Jesus was to stay away from marriage.
http://www.holyspiritinteractive.net/columns/williamsaunders/straightanswers/48.asp, The Gnostic Gospels: The Washington Post religion section recently had an article about the Gnostic gospels. What are they?:
This teaching impacted their morality. On one hand, since material things were considered evil, many Gnostics refrained from eating meat, marriage and conjugal love (because one would not want to imprison another soul). On the other hand, since a person who had the gnosis and was under the influence of the spirit was assured salvation, some Gnostics lived licentious lives of debauchery.
http://members.aol.com/SMARTNEWS/Sample-Issue-9.htm, SMARTNEWS's Issue #9 - 7/96:
The following article discusses the book "CULT AND RITUAL ABUSE - Its History, Anthropology, and Recent Discovery in Contemporary America" by James R. Noblitt and Pamela Sue Perskin. …
In the chapter on Investigating Western Occultism, the authors discuss the mystery cults and Gnoticism ("various sects...based on a dualistic concept of good and evil as relatively independent forces in the material and spiritual universe..." pg. 96) Some Gnostics were accused of "...ritual cannibalism and communal sex acts.
http://www.chaosmatrix.org/library/humor/thelemic.txt, A THELEMIC LANGUAGE LESSON:
18.There were 3 major philosophical schisms, 2 magical duels to the death, an impromptu X-rated Gnostic Mass, and the usual orgy to follow.
http://www.acns.com/~mm9n/7churches/seven_churches6.htm, The Seven Churches: A Study o the first three Chapter in Revelation:
2. Nicolaitans were a sect who encouraged Christians to engage in idolatry and immorality
It must have been a direct consequence of the loving caring church as a unity. So Nicolaitans introduced[sic] sex orgies as an expression of Christian love in their love feasts. Sex is hallowed by God as an expression of faithfulness and love and as an experience of Heaven and its joy as a result of intense personal unity.
Encyclopedic Dictionary of Religion, 1979, vol. 2, p. 1506, “GNOSTICISM”:

Especially the extreme obvious part where “Jesus” condemns marriage: Matt. 19:10-12; Luke 20:34-36; 1 Timothy 5:11-12.
http://chronicle.com/colloquy/2006/05/gnostic/ (The Chronicle of Higher Education), The Lost Gospels:
“The Guest”:
Karen L. King is a professor of ecclesiastical history at Harvard University's Divinity School.
“Transcript”:
Question from Nick, Surrey:
Some other early Christians accused the Gnostics of
being sexual libertines. Was there any
truth to the rumor or was it just a useful form of defamation.
Karen L. King:
This question is much debated among scholars. The new
literature we have found, despite its considerable diversity, tends toward
ascetic positions of various kinds. Let me hasten to add, some of these present
marriage and sexual reproduction in a positive light, so we can't confirm the
stereotype of "Gnostic hatred of the body." But we also find no evidence of libertinism. That could be
because it belonged to strategies of slander or because of the selectivity of
what was preserved. Many scholars, myself included, wonder whether the charge
of libertinism represents a (more or less purposeful) misrepresentation of
certain practices, much the way that the Christian practice of Eucharist was
behind charges that Christians were cannibals.
Of course.