Well, eating an apple would be morally acceptable because it is obviously a food--food being necessary for survival--and is apparently not poisonous or harmful, unless ingested in large amounts.
So your rationales for considering something "morally acceptable" are:
a. it´s necessary for survival,
b. it´s not harmful?
Is that the complete list of criteria, or are there any more to come?
I don't know of any evidence that extra-marital or contracepted sex is necessary for survival.
Eating apples isn´t necessary for survival.
As far as the tree issue... your basic approach seems to be to claim--without evidence--that you have no position, and that I am the only one obliged to offer evidence, which may be rejected by you at will, as if that proves that evidence has not been provided.
No, that wasn´t the point of the tree-thing. The point of the tree-thing was that it´s - despite your claims to the contrary - very easy to convince people of the existence of a tree, but not so easy to convince them of your "moral" convictions. E.g. you needn´t appeal to your own "intuitive reasoning" when it comes to the existence of trees, but you obviously need to do it when it comes to your "moral rights and wrongs".
And, yes, you have made bold claims about the "immorality" of something and even went out an a limb and called your opinion "objective". That puts the burden to substantiate this position on you - or else it wll be filed under "pat´s unsubstantiated personal subjective opinion".
Since I have never made any such claims either way (and, on top, would never confuse my opinions for "objectivity"), I have no such burden.
That´s what you get from being loudmouthed.
Likewise, if you were here, I could show you the tree in my yard and you could deny that the tree is there.
Has that ever happened to you?
It may sound far-fetched, but not so far-fetched when compared to people not seeing the intrinsic connection between sex and children, or people not knowing that people of the same sex can't get married, etc.
Cool. Then post a picture of this "intrinsic connection", or invite me to a place where it´s exhibited. Rather, the fact that there are reliable means of contraception disprove such an "intrinsic connection". If it were intrinsic, it would work all the time.
As for same sex marriage: Where I live people of the same sex do can get married. I can show you the laws, I can show you documents, I can show you pictures.
Thus, when talking about denying the existence of a tree in my garden despite manifest evidence, this seems to be more like your position when it comes to the existence of same sex marriage.