Your explanation might make sense in a perfect world... but we do not live in a perfect world. We live in a fallen one. Where disease and illness can strike anyone. And so when an infertile husband and wife turn to modern science to give them the child they desire, who are you to tell them that God says they shouldn’t have a child? I believe that God decides, not us.
Infertility means you've got some sort of disease or injury or malformity that makes you unable to have childen through normal intercourse, and it should be addressed by the medical profession with the ethical goal of curing the disease, healing the injury, repairing whatever is getting in the way of naural fertile sex.
Surrogacy does not cure infertility: Mr. and Mrs. Romney are still apparently inable to have children through normal intercourse.The morally upright thing to do, is to seek medical help to cure their infertility. There are effective drugs, devices, and surgery which can often address that problem, and restore their healthy sexual function.
Nobody's against actual CURATIVE medical inervention.
What's wrong is going outside your marriage to impregnate another woman.
LOL, I suppose it's entirely possible that God DID tell the "infertile" couple that they shouldn't have a child.
It seems more that people like you are the ones saying they should.