I have trouble finding "lay lady lay" offensive.
Unlike 'stand by your man' there is no indication that the woman is being pressured into staying in a bad situation. (The man's hands are 'clean' afterall).
There is a greattenderness and affection being sung to the woman by the man.
And while the song is likely about sex, you can also read this part as a marraige proposal:
Why wait any longer for the world to begin
You can have your cake and eat it too
Why wait any longer for the one you love
When he's standing in front of you
I think it's beautiful. I wish I could write a love song like that.