If it were impossible to be married to a harlot, then yes, I’d agree with you that, lacking a better fit/understanding, it by default must mean to have sex.
However, we all know that it is entirely possible to marry a harlot leaving us with two options to examine.
Quite simply, I see it as saying 1. You shouldn’t fornicate with a harlot as thats a sin against yourself per Proverbs 5, and 2. you shouldn’t bind/glue/join/marry yourself to a harlot as that means you are bringing someone into the family of God that brings dishonor to him.
I do not believe that these are a singular issue, rather two separate issues, even though I was raised to believe that it was the same thing. After studying it and comparing it to scripture, I just cant make the Scriptural evidence connect it to sex even though I’ve been assured by those who should know that it must somehow. (I’m not referring to Zec or anyone else here)
First, as
@ZecAustin has pointed out, the immediate context both before and after is clearly talking about fornication (see v13 and v18). Secondly, I don't see where you get two separate statements out of it, it seems to be talking about one thing to me - which part of these verses relates to 1 vs 2?
Now, considering that context, let's look at the passage and consider the potential options for its interpretation.
1 Cor 6:15-17:
Know ye not that your bodies are the members of Christ? shall I then take the members of Christ, and make them the members of an harlot? God forbid.
What? know ye not that he which is joined to an harlot is one body? for two, saith he, shall be one flesh.
But he that is joined unto the Lord is one spirit.
I have bolded the key words that we need to consider the meaning of.
Harlot:
Clearly includes a prostitute. However, Thayers lexicon states: "
properly, a prostitute, a harlot, one who yields herself to defilement for the sake of gain (Aristophanes, Demosthenes, others); in the N. T. universally, any woman indulging in unlawful sexual intercourse, whether for gain or for lust:" So, if that is correct, this word includes any slut, any promiscuous woman, not just a woman you pay for sex. On the other hand, given the context of the idolatry of Corinth, and the clear spiritual nature of this passage, it could refer very specifically to a temple prostitute only. So there are three possible meanings to consider:
1) Any promiscuous woman (paid or unpaid)
2) Any paid prostitute (religious or secular)
3) A temple prostitute specifically
Joined
The two meanings suggested are
1) Sex
2) Marriage
One body / one flesh
Two different words for body / flesh are used, both emphasising the physical nature of this statement. This has been suggested to mean:
1) Sex
2) Marriage
3) Something else?
@Verifyveritas76 suggested that joined = marriage, in which case this must mean something closer still, but I'm not sure what that would be.
Further, we know that marriage to prostitutes is not forbidden elsewhere in scripture. Priests were not to marry prostitutes, but apart from that marriage of prostitutes is never spoken against and seems to be encouraged (see examples of Rahab and Hosea). In general, marriage is the solution for sexual sin, and who more than a prostitute requires such a solution? It could be taken that we are all intended to be priests so all forbidden from marrying prostitutes - but that would mean that all prostitutes were now denied the possibility of a Godly husband, so that doesn't fit with God's nature. However, it may mean you can't marry a prostitute that keeps being a prostitute after you marry her.
I'm still pondering what to do with that, but I hope that it helps others to frame the issue a little more clearly.