The fact that she is your wife is not a reason to believe that her consent is not necessary anymore. She has right to say no if you try to have sex with her. She is not your property. She is not your slave. She is your wife.
The right to refuse stems from the natural logic that sex is a consensual and participatory team act. Both parties must participate in it. Consent is the foundation of participation. It exists not only at the beginning of sex, but also throughout the act. It is the power of consent that enables a woman to tell you how it pleases her, the best position, and generally how to do it. It is the power of consent that enables a woman to tell you when it hurts and when it pleases. It is the power of consent that gives meaning to participation. Indeed, it is the woman's right of refusal that makes it possible for a normal man to enjoy sex.
Without that right of consent, voluntarily given by the woman, you are a thief, taking what does not belong to you. Iif she is your wife, then you are a petty thief. It is the fact that she could have refused if she wanted that makes you proud when she says yes.
The right to refuse is important in many other ways. It enables a woman to convey to you what pleases her and what doesn't please her in general. If you behave bardly toward the woman, she will withdraw her consent as an incentive structure to check that behavior. The fact is that the man should do more of those things that encourage her to say yes, and less of those things that cause her to say no. Through that incentive structure built into the relationship dynamics, a woman is able to exact some influence over her man. To suggest that a married woman does not have the right to say no is to take away one vital God-given incentive modulator in humans.
In fact, a frown from my woman makes me nervous. It means she is not happy and I freeze on my track. I cannot proced until I find out why she is frowning. You cann't ignore that frown, It is important to always allow the right to say yes or no even to the wives. If you abuse your wife or maltreat her or fail to please her, expect her to say no to sex. You must have a way to negotiate for sex. Send her flowers. Send her poems. Do whatever you can. Trick her if you wish, though I don't encourage obtaining by trick. But never force her. And please don't make the dumb argument that she is your property, because she aint.
Also, she can withdraw her consent in the middle of the act and if she tells you to stop, you have only a few seconds to pull out and beg.
EU