Shamelessly hijacking the top comment.

I have a Th.M. in New Testament and an M.Div in New Testament from Princeton Theological seminary; enough to be accepted as an "expert" for the purposes of an r/AskHistorians AMA a year ago. This TIL is either "completely wrong," or "probably wrong." 'Aρσενοκοίτης, the word in question is literally a portmanteau of the word for "man" (arsen) and the word for "bed." While Paul is the first person in the literature to use this word, assigning it an ambiguous or uncertain definition struggles for three reasons:

1. Although a standard ancient practice was to send a "reader" with a letter to help explicate and clarify the author's meaning (to satisfy the concerns surrounding ambiguity in what we would today call "semiotics," cf. Plato's Phaedrus), the portmanteu may have been self explanatory without this person's aid. For example, it would be silly to claim that if some chav called you an "bumbanger" that what they were alluding to was ambiguous or unclear because that term does not appear in any English dictionary.

2. Paul, though almost certainly versed in Hebrew, seems to quote the Greek translation of the Hebrew Bible most often, as he is writing to Greek audiences. Compare the Hebrew Bible's text of Leviticus 20:13

Here it is in English:

"If a man lies with a male as with a woman, both of them have committed an abomination; they shall surely be put to death; their blood is upon them."

And in Greek:

καὶ ὃς ἂν κοιμηθῇ μετὰ ἄρσενος κοίτην γυναικός βδέλυγμα ἐποίησαν ἀμφότεροι θανατούσθωσαν ἔνοχοί εἰσιν.

Note the similarity to 'Aρσενοκοίτης in Corinthians, it's literally the portmanteau broken apart to express the idea of lying (in the OT, usually an allusion to "having sex with") with a man "like a woman." So the argument that Paul is simply glossing this probably well-known verse to show the new Gentile (non-Jew) converts that their cultures acceptance of casual gay encounters is not acceptable is very strong.

and

1. Given the radical abhorrence of the Jewish culture for homosexual acts (at least on paper, the punishment was supposed to be capital, though scholars have good reason to doubt whether the harsh punishments of the OT were ever actually carried out, or were written retroactively to express the sort of radical holiness that the religious thought should be practiced), it is far more likely (as argued by many pro-GLBT scholars, such as Robert Jewett) that Paul simply dismisses them all with a hand wave rather than singling out "molesters." Paul's condemnation of lesbianism in Romans is particularly potent in this regard, lesbian pederasty is not well established in this period, as far as I know.

Now, does this mean that Christianity is duty bound to oppose homosexuality in all forms, always? Maybe, but there are at least three (surprise surprise) things to consider along with that:

1. The verses only condemn the sex act. The ancient world had no concept of sexual orientation, so the notion that "being gay" is a sin, like that ten-year-olds experiencing SSA should be condemned and made to change, is a modern one. If you're not having sex or lusting, you're not falling afoul of anything in the Bible as a gay person, even by the most literal reading.

2. Paul's argument in Romans, considered the seminal work for understanding his theology, hinges on the fact that homosexuality is unnatural. We know now that that's not the case, so a compelling argument could be made that the related pronouncements suffer from a lack of human insight, the way that the creation account or flood story depend on assumptions about the natural world that we know to be flawed.

3. Paul may not have known of any instances of lifelong monogamous gay couples, since the notion of homosexuality as an orientation rather than an act didn't really exist. Many Christians argue that the Christian sexual ethic (chastity in singleness or sexual expression in lifelong monogamy) could apply to gay couples as well, who might have been accepted by Paul and Jesus (and the writers of the OT) if their constructive relationships (and a dose of personal piety to boot) had been observed in antiquity.

As a scholar, I'm not going to suggest which side of this issue anyone should come down on, but that's just some data for you to consider.