No, we don't wonder where liberals get that idea. Liberals came up with the idea themselves. They have been prying into bedrooms for generations now. They have been very effective in capturing the territory and any opposing view is seen as a serious threat. Population control groups, fem-nazi's, pharmaceutical companies, latex corporations, etc., etc. All have a stake in keeping the awareness of natural law and Christian morality under wraps. It is a typical liberal ploy to cry foul, when what they protest is exactly what they practice. So complete is their victory in this arena, that even conservatives have bought into the lie.
Not only do they want into the bedroom, they want to post "sex police" at the door to keep watch that your not engaging in activity that they disagree with.