While sex is important in a committed marriage, it is not the only thing. If you take God, family, and commitment away from a marriage and make it all about sex it will fail. Take away sex, even while leaving the rest, and it will also probably fail.
Living your life around a sexual point of view twists these people.
I disagree with you slightly -- the primary points of marriage are to be God and commitment.
Sex and family may come and go -- what of severely disabled people or very, very old folks? Companionship and God are still there
The problem is when we removed sex from being a component (and not the most important one) of a marriage to be JUST about fun (note: just -- sex should be enjoyable, but should not be just about enjoyment).
By going down this route we said ok to contraception "to prevent mistakes" and for the 5 to 10% of "mistakes", there is the "mistake-corrector" aka "abortion" and if not then "welfare single-mother" and "free to have sex with multiple partners, fathers"
And to avoid this, why not gay sex? it's all related. Plus the ease of getting a divorce "on irreconcilable grounds", societies acceptance of "shacking up" to the extent that if one does NOT do this, then one is considered abnormal etc. etc.