I am not a romantic person and I am not married nor will I. As far as DD marriages, I view it as a combination of paraphilia (spankophilia) and dominance/servitude. It is a relationship dynamic where one knows who is boss and who makes the rules. If one is in an uneven marriage such things as M/s, vanilla D/s and DD are practical as it just enforces what is already present. I have a friend in such a position, her marriage was uneven and she preferred it such and is now a hardcore S&M freak.
Sex nor Marriage is my sort of things but if you have a working system adding a factors such as these could only build upon it.
If a woman or man is subservient to the other partner then what can be more natural then to incorporate a relationship dynamic which rectifies this even more?
I wouldn't want to be in that kind of relationship- I see a couple as being equal partners. But if both people of the couple agree with it, then they go for it. (If both parties don't agree with it, it is abuse).