Here is a crazy woman arguing several insane points:
1) A wife has a duty to initiate sex with her husband.
2) A wife who withholds sex from her husband is emotionally abusing him.
3) A wife who withholds sex from her husband is breaking her marriage promises.
...and I happen to agree with her.
I also believe you can swap husband and wife in each point above and it holds true the other way.
We need to start seeing the withholding of sex within marriage in the same light as other forms of sexual infidelity (e.g. pornography, affairs with others), because they are all forms of adultery.