I agree that they just cannot go there because if they do, that is way too far for even Demon!Dean. I'm an avid Buffy fan and they went there with Spike, but he had been a monster for over a century and a half. I was okay with the way they handled it. Those writers had to push him almost beyond redemption in order for him to really earn it when he gained a soul and helped save the world. But, speaking of souls, Spike was a soulless demon when he attempted to rape Buffy. Which brings me to...
What is the status of Dean's soul? Does Demon!Dean have a soul? (I remain unconvinced that he's cured of demondom.) Or as others have postulated, being a demon twisted his soul, and now that he's "cured" his soul is back to normal?