This age old example perfectly fits on your logic. People buy knives to use as a kitchen utensil and others buy it to kill other people so we should ban making , selling and buying of all kinds of knives ?
What treatment of surrogate mothers has to do with it being a legitimate practice of allowing people to have kids if they cannot conceive ?
There are some who will treat the surrogate mother with respect. Also surrogate mothers normally agree to it for the love of family , out of their wish to help other fellow humans who are in suffering emotionally because they do not have kids of their own.
I know it's not the same issue of course, but this example reminds me of the Quranic telling of the creation of Adam and Eve, in which Allah SWT tells the Angels of the creation of mankind and His desire to put them on Earth. And how the Angels respond by describing all of the destruction mankind will cause, and Allah SWT responds by saying, "I know what you know not." I believe that's Sura 2, verse 30. It's one of my favorite passages to think about when I read the news; just because mankind was going to cause destruction doesn't mean their creation wasn't worthwhile. Just because something bad COULD/WOULD/DOES happen, doesn't mean something good couldn't/wouldn't/doesn't.