Not all mothers may feel it (I certainly didn't feel any particular bond with my children when pregnant- nor did I feel the much vaunted 'rush' of love), but the infant certainly does. That's the key point. The infant is bonded with its mother from before birth
Fetuses do experience "stuff" before birth (they can recognize their mother's voice, for example), but if there were any important or lasting bonds from the fetus to the mother, we would expect to see data coming back showing that children created through gestational surrogacy have higher rates of psychological issues.
They do not appear to.
(See links posted upthread)
So far, the statistical outcomes (things like rates of trauma, behavioral issues, school dropout rate, criminal behaviors, going off the rails as a teenager) of GS kids appear to be about the same as those from "regular" families of similar demographics, and do not at all resemble the complex issues and challenges which tend to be widespread among adopted children, which suggests that the higher rates of issues found among adopted children are caused by other things (issues in genetic bloodlines, abuse/neglect, alcohol and substance injury in utero) and not by disconnection from the birth mother per se.
Surrogacy is quite new and I suppose it's possible that these GS kids will suddenly start developing terrible psychological issues in their 20s or 30s or whatever, but frankly, if that was going to happen I would have expected to see some sign of this by now.
I suspect that as the data continues to show GS kids turning out just fine, most of the objections to altruistic surrogacy will fade away (just as opposition to things like gay parents adopting have gradually diminished as the data has come back showing that they turn out no different to those adopted by straight couples).
Commercial surrogacy is a different matter, but I think the issues are about women's bodily autonomy rather than potential psychological issues in the kids. The kids themselves will likely turn out just fine.