There are several important issues that must be addressed when trying to understand Greek/Roman homosexuality, and how it influenced the New Testament writers. First, until recently, many people believed that the only type of homosexuality Paul would have known about as he wrote his letters, is pedastery. Pedastery is a custom that is practiced in many cultures, but is very much absent, and even offensive to most Western cultures. In the Greek world, an older man, an erastes would take on an eromanos, a boy between 12-18 (after onset of puberty), as a student. The relationship that was expected to occur by the parents, and both erastes and eromanos, involved the man teaching hunting, warfare, adult male customs, etc., to the boy. An integral part of this relationship was anal or intercrural intercourse, with the teacher being the active partner and the student playing the passive role. The rationale of this is two-fold. First, in Greek culture, semen contained important spiritual, masculine qualities, such as arete (virtue), power, etc., that would be passed on to the student during the sex act. Second, social roles were demonstrated. Females had no rights in Greek culture, and were considered property. In the Greek mindset, men's dominance of women was a part of nature, and must be expressed in every aspect of the male-female relationship. In the erastes/eromanos relationship, the teacher is the dominant player, and must subjugate his student. In this way, the student is inculcated with skills in domination. Regardless of our cultural judgment on this form of ritual propagation of ideology, this was a large part of Greek culture, especially in certain geographical locations. 

It has been thought that this was the only type of homosexuality that Paul knew when he wrote his letters. This, however, has been shown to be incorrect. Several authors, such as Dover (2nd edition), Boswell (1994), and Smith clearly show that pedastery was not the only form of homosexuality known in Greek and Roman culture in the first century CE. Smith and Boswell especially give numerous examples of homosexual relationships that are not age-structured, and that are based on mutual consent. Moreover, we find that both Roman and Greek cultures accepted homosexuality, and at times instituted it in non-pedasteric forms. For example, Polybius (2nd century BCE, Rome) reports that "most young men had male lovers" (Greenberg, p. 154). Further, "many of the Roman emperors had homosexual tastes," and "in Greece, sexual preferences were frequently not exclusive," to the inclusion of Julius Caesar (Cato: who states that he was "every woman's husband, and every man's wife"; pg. 155-56). At any rate, it has been argued by some that Paul's use of arsenokoites and malakos is for lack of a better expression for homosexuality in general. The argument is that Paul wanted to condemn not only pedastery, but all forms of homosexuality, so he could not have used erastes/eromanos because that would have apparently limited his condemnation to pedastery. However, current scholarship indicates that the terms erastes and eromanos were not used exclusively for the boy-man, subordinate-dominant relationship. On the contrary, these terms can refer to a relationship of long-lasting duration and equality between partners. 

This brings us to our second point, which is that Paul's intentional meaning for the word arsenokoites is far from clear. Paul had many different words at his disposal that referred to homosexuality in general, not just pedasteric relationships, as was once thought. In this line of reasoning, Paul coined the term from the Septuagint, as discussed above, because there was no word that expressed all homosexual acts, regardless of the type of relationship. This is now known to not be the case, so we must search further for the meaning of this word. The best way to learn the meaning of this word is to look at its usage in other contexts. The problem is that we primarily find arsenokoites in lists, which give us little information as to the meaning of the word. A search of the Thesaurus Lingua Graecae database as of 1997 shows 43 usages (you can feel free to e-mail me for these references). All but one of these are in lists that are of the same basic pattern as that found in 1 Corinthians 6:9 or 1 Timothy 1:10, using mostly the same words. The one not in a list is found in Scholia in Aristophanem (Work 014, sch plut.153.5; TLG), mentioning the Athenian way of life (entautha diasurei ten twn athenaiwn diagwgen, hoti esan arsenokoitai dai phauloi.), which also is of little value. 

The only other option we have is to try to discern some meaning from the use of arsenokoites in the lists. Martin notes that "sin lists" tend to congregate words of similar type together. For example, "first are listed, say, vices of sex, then those of violence, then others related to economics, or injustice" (pg. 120). In most of the TLG listings, the order is fairly standard (but not universal): , pornoi, moixoi, malakoi, arsenokoitai, kleptai, pleonektai, methusoi, loidoroi, with some substitution of andrapodistais kai epiorkrois following arsenokoites. Translated, the pattern is as follows: temple prostitution, adultery, moral weakness (malakos), arsenokoites, thief, greedy, drunks, foul-mouthed; or arsenokoites, slave-trader, perjurer. In the TLG lists, the division is not very clear, other than the first half of the list seems to be sexual, then arsenokoites is listed, then economic/injustice sins, sometimes followed by moral sins. If this were all we had, then we would not know on which side to classify arsenokoites--whether purely sexual, purely economic, or some mixture of the two. However, there are two non-TLG texts, both of which are early usages of arsenokoites, the first of which is from the Sibylline Oracle 2 
 

"Do not steal seeds. Whoever takes for himself is accursed (to generations of generations, to the scattering of life. Do not arsenokoites, do not betray information, do not murder.) Give one who has labored his wage. Do not oppress a poor man." (Martin, pg. 120)

Similarly, the second text, from the Acts of John 36: 
 

"And let the murderer know that the punishment he has earned awaits him in double measure after he leaves this (world). So also the poisoner, sorcerer, robber, swindler, and arsenokoites, the thief, and all of this band..." (Martin, pg. 121)

In neither of these texts do we find them in the context of purely sexual sins. In fact, we see no hint of sexuality at all in these lists. We do know, however, that arsenokoites is some type of sexual sin. However, if we put in the English translation "homosexual" in place of arsenokoites in these lists, it makes no sense. It doesn't fit with the categories. What makes much more sense, is if the placing of arsenokoites in the TLG texts in between the sexual sins and economic/injustice sins is not an accident. What makes sense is that arsenokoites is a term referring somehow to sexual injustice. For example, when arsenokoites is placed just before slave-trader, this seems particularly appropriate, since homosexual slaves were normative in both Greek and Roman societies. The interpretation of arsenokoitai therefore, as one of homosexual subjugation and/or exploitation, rather than referring to all homosexual behavior, seems most appropriate as we see from these contexts. 

This type of connotation to arsenokoites fits well within two other non-TLG texts, both of which are very early uses of the word. The first is out of the Apology of Aristides, chapters 9 and 13. It is relays the myth of Zeus, and his relationship with the mortal Ganymede. In the story, we are told that the myth is evidence that Greek gods act with moixeia (adultery) and arsenokoites. Similarly, in Hippolytus' Refutatio chapter 5, we are told the story of the evil angel Naas, and how he committed adultery with Adam in the Garden, which is how arsenokoites came into the world. Hippolytus relates Naas and Adam back to Zeus and Ganymede (Petersen, pg. 284). In neither of these instances do we find a mutually consenting, equal relationship--we find a powerful aggressor subjugating the weak. This human rights violation (in modern terms) gives arsenokoites the meaning that makes sense in the few contexts/lists that we have.