I think the first thing we got to look at is what does Zina means as that is the word used throughout the whole Quran time after time.
Regularly it means both Fornification and Adultry thus covering both ends. I've seen people challenge that word before but never seen a fully convincing argument on it. Maybe we can finally crack down and be 100% sure on things 
I personally believe that it does mean both those things because 23:3-23:4 state you gotta guard your private parts except around your wife or MMA.
So I lets begin talking on if its truly allowed or not without any idea of morality in on whether "its not nice" or "its wrong" or "its dirty" or "it gives STDs" forget all those and lets straight up just talk on if its allowed or not, which my personal view is that Zina means both those as that is what it means since classical arabic times as well as 23:3-4, but lets see what you say
This was not my aim for this topic. I will quote my earlier post and add on to it.
The key is to understand that morality is not intellectual and logical. If I ask for an example of evil, one will give me an answer such as ''murder'' or ''thievery'', but this just a verbalization of our emotion, because these are not logical explanations, we cannot intellectually differentiate evil from good. The sphere of the intellectual and the emotional are different, as much as one cannot explain why X was sad on the day Y mathematically, one cannot say that this act was evil or good based on a bullet-proof intellectual fact.
Thus, the peasant and the aristocrat will both systematically agree upon what is good and what is not, regardless of what they have or have not read. Upon this understanding, one will systematically arrive to the conclusion that the only law to be adopted is the one that is universal and appertains to each and every human being that is born on this earth, regardless of his class.
This is why I insisted on giving exclusively moral arguments, as Allah's sunnah does not change, the "rules" within the Qu'ran were to be followed from the first morally developed human beings. A time where there were no STDs, etc. Secondly, I prefer not to try to understand what is what based on the translations of the Quran, as they are an absolute mess. It is said in the Qu'ran that we have numerous examples in the universe, the animals and ourselves as well; and interesting fact, some animals are noted to be promiscuous...
I will give you an example: We have always thought that homosexuality was seen as an abomination quranically. I have never been able to find any reason for it morally. Upon research, I understood that a great number of species are homosexual or bisexual. Upon some more research, I understood that we have archaeological proofs (carvings etc.) proving there were previous mobs, before the one of Lot, that practiced homosexuality (and thus the "crime" of the people of Lot was not homosexuality because it is said in the Qu'ran, that they practiced something which has never, ever, been done).
I hope you get the idea...
