I don't know about rewardinig socially unacceptable behavior but I can say this:

In some of the cases that I read about on the board I can understand the D person needing space.
In other cases I think the D person is really just taking advantage.
Just because a person is D does not mean that all of their actions are governed by the D.

You know what, if someone can go out every night to bars and find someone new to mess around with then they can certainly find it in them to work on the relationship that they are already in.
If someone can find it in them to do what they want to do but when it comes to acting responsibly and caring for their family they suddenly can't function because of the D...that to me is taking advantage.

And if someone tells them "Okay, we can be in a relationship but you don't have to spend any time with me or talk to me unless you want to and that's okay because you are D", then yes, you are reinforcing their negative behavior and telling them that it is okay to use their D as an excuse.

I tend to get quite angry at the D people who use it as an excuse because they make it harder for most mentally ill people who are really trying hard to take responsibility for themselves and learn to live as highly functioning adults despite their illnesses.