Anything that turns a human being into a commodity to be bought or rented, even if some people find the arrangements work for them, is pretty repugnant to me and imo shouldn't be supported in any form from a public policy perspective. More so when it disproportionately impacts one class of people.
The fact money is involved immediately creates a power imbalances that spills over internationally. I can't put too much stock in studies of US surrogate mothers that don't also consider the views of surrogate mothers from countries that have been used as 'destinations' for cheaper surrogacy arrangements eg Thailand, India, or Ukraine, who have been hired by US couples, it's only part of the story (and is almost certainly the happier side).
I also find the language very dehumanising. 'Surrogate' rather than 'mother' or even 'surrogate mother'. In some articles/conversations it's just the 'uterus' that is discussed (in the context of ‘implanted into the uterus’), ‘carrier’ or the 'vessel'. Language like that is intentionally used to help shape the narrative and lessen the role of the surrogate mother. We should be able to talk about it properly.
Regardless of whether the contracts are legally enforceable, they are designed to make women feel like they don’t have control (which, in turn, psychologically does impact the degree to which someone will argue with a decision being imposed on them). I imagine it would be incredibly difficult for any pregnant woman to suddenly decide they were going to renege on the ‘agreement’ due to expectations and societal pressures. If we were talking about anything else I don't think we'd call it consent.
Even 'altruistic' surrogacy comes with a host of issues as haawa's story shows.
On top of that there's the risks to the child which other posters have explained more knowledgeably than I could.
Unless and until surrogacy can be regulated to be perfect (e.g. no exploitation of any women whether financially or emotionally, clear evidence there is no risk of emotional damage to the child) I just can't agree with it as a concept. Infertility must be heartbreaking, but I don't think it is a valid reason to create and prop up an industry that puts women globally at risk of death, serious injury, or exploitation, or children at risk of deep psychological issues.

for you @haawa. Your story is truly heartbreaking. Thank you for sharing it with us.