I'm not as black and white about it as some on here.
For me there are two issues. The potential exploitation of the surrogate and the potential trauma for the baby in being removed from his or her birth mother.
On the first issue, I do accept that there are certain situations in which there is no exploitation and little risk, but they are few and far between. Even where it is an altruistic surrogacy and the surrogate mother really, genuinely wants to carry a baby for a couple she really cares about, there are still risks. What if the baby has a life limiting condition and the surrogate and the intended parents don't agree on whether she should terminate the pregnancy? What if the surrogate, having had previous uncomplicated pregnancies, ends up with a life threatening pregnancy complications, severe birth injuries or even dies in childbirth? How would you ever forgive yourself? But in the vast majority of cases I think there is clear exploitation and the surrogacy industry is really problematic. Even in the US where using a surrogate might cost you $250,000, the surrogate only gets around $40,000, which is really not a lot of money for what she is actually doing for the couple. Most of the price tag goes on medical bills and agency fees.
And then once you've normalised the idea that it's OK for a rich couple with €250,000 to spare to use a commercial surrogate because it's all been done properly and the surrogate hasn't been exploited, you normalise the idea that commercial surrogacy is OK among people who haven't got €250,000 to spare but think, "Why should this option only be available to super rich people like Chrissy Teigen and John Legend? I deserve to have a baby as much as they do. More so, actually, since they already had three. I can't afford to do it here but I can afford to go to Ukraine and do it there."
The second issue, about the impact on the baby, is just too unknowable. All we have is speculation really. Obviously I hope that all babies born to surrogates have wonderful childhoods with loving parents who went to extreme measures to have them, but who knows what the impact of being removed from their birth mother really is? It's not like adoption where they are being removed from their birth mother for their own welfare, and where they haven't been conceived for the purpose of being removed from their birth mother and raised by someone else.
Like I said, I'm not completely black and white about it and I would have some sympathy for, say, a woman born without a uterus who was desperate for her own baby and did everything she could to respect the welfare of both the surrogate and the baby. To me that's far less clear cut than celebrities who already have several children using a surrogate to have even more.