Surrogacy

How ethical is surrogate motherhood when there are thousands of children waiting to be adopted in our own country alone. While it is understandable that an infertile couple would desire to have children, from what I understand only the father is related by blood. Although the adoptive mother can have close contact with the surrogate mother, she is still adopting the child. So how is it that woman are paid to create more children when so many are already out there wishing for a loving home?