Where consent is most problematical is when the sex is "casual," meaning in the context of a casual relationship or no relationship at all. Which I can understand in theory but can't personally relate to.
As you point out in your excellent article, however, there are layers upon layers of consent, from complete enthusiasm to the things one does just out of love for a deserving partner.
Good communication is the key, along with a sincere commitment to one's lover's pleasure and well-being. If my partner never tells me no, how can I be sure she's really into it when she says yes?