Here is a Christian point of view of such a "standard" offered yesterday by FreakyKBH [on the "What if...?" thread]:
"Sexual relations are meant to be shared with one person and one person only throughout their lives".
I personally go along with this as my "standard" but only after choosing a mate and making that monogamous commitment to her. So, I do not subscribe to the notion that having 'only one sexual partner throughout life' is something that can be called "sexual purity".
In fact, "sexual purity" strikes me as rather opaque terminology and is perhaps best replaced with "sexual morality" for the purposes of this OP.
Putting to one side the "sexual morality" of pedophiles, rapists and perpetrators of domestic violence [and so not trying to include them in any consensus]...
and putting aside ~ for the sake of discussion ~ the notion of a supernatural being being concerned with people's sexual relations [though I eyes-openly accept that there will be posters who will not want to put it aside for the sake of this discussion!]...
What consensus can be reached by Christians and non-Christians alike about what would constitute a common [shared] and common sense view on the morality of sexual relations?
I would suggest:
Do not deceive your partner. [e.g. Lies, false promises, misrepresenting circumstances, intentions, the past, commitment, feelings etc.]
Do not coerce your partner. [e.g. No emotional blackmail, no violence or use of strength to negate the issue of considered consent, no undue pressure to go from a non-sexual relationship to a sexual one]
Do not harm your partner. [e.g. knowingly spread STDs, create children that one is not willing to take responsibility for, betray or cheat, or abandon after obligations have been entered into]
Can we pretty much all agree that these three 'rules' provide a basis for a consensus regarding a practical "morality" to govern behaviour in sexual relations [and one that Christians and non-Christians could share, supernatural imperatives aside]?