Part of the question should be, "Is it a crime for a marriage partner to deny sex to the other partner when the other partner requests (demands) it?" And if it is a crime, is it always a crime? Or are there certain circumstances under which it is a crime, while it is not a crime under other circumstances?
Interesting view.
Even if it is a crime to deny sex, the punishment should be divorce / partner walking out. Definitely not rape.
Walking out momentarily, perhaps. But not permanently.
When people live in a marriage relationship, they live in possibly the closest relationship of any. Sports team players don't live that close, even when they are executing well-practiced plays.
The point is. Each partner in a marriage relationship is going to have different ideas than the other at times. How much denial is one supposed to put up with from the other? How much rape is one supposed to put up with from the other? Rather, they should both live up to the marriage agreement.
The marriage agreement, especially if it is not written, includes abstinence at times, and indulgence at other times. At times the one wanting sex should bow to the wishes of the one not wanting sex. At times the one who does not want sex should bow to the wishes of the one who does.
Unfortunately the world is not all that friendly all the time. Is it a crime? Perhaps. Is it their business? Yes. Was it in the marriage agreement? In some marriage agreements. Should government intervene? Yes, if government was in the agreement... and if the agreement is broken, possibly.
This whole question must be applied on a case by case basis. There is no one answer that fits every case, no matter how people on the outside feel about what goes on between a married couple.
Another consideration is the idea of illness. An overwhelming desire for continual indulgence, or an overwhelming desire for long term abstinence, might be indications of mental or physical illness in one or both of the partners. Is illness a crime?