So this is a tricky question for a few reasons. One is that we typically don't have the views of the surgeons unless they were also the person ordering the sterilizations — which in some cases was the case, because of how some of these hospitals were run in the early 20th century. The other is that different states had very different procedures and rationales for ordering sterilizations; there was no unified, federal approach. So this question, like many others regarding compulsory sterilization in the United States, is likely to break down differently on a state-by-state basis, and, depending on how the state system is set up, on an institution-by-institution basis.

A million eons ago (translation: about 20 years ago) I did a lot of research into how compulsory sterilization worked in California, the most-sterilizing of the states, and what I found was that because of the way the California sterilization law was constructed, and because of the way in which the California mental health system was set up prior to the 1950s, the medical superintendents at the various California institutions that could order sterilizations had almost total autonomy in the decision of whether to sterilize and why to sterilize. As a result, when you look closely at the institutions that either did a lot of sterilization or no sterilization, you find that there were people there who ran the institutions for a long time and had strong opinions on the matter. Interestingly even the ones who sterilized did not necessarily embrace eugenics as their main motivation — in one hospital, for example, the medical superintendent subscribed to a crackpot theory about how sterilization would provide therapeutic value to patients. But in the sterilization-permissive atmosphere of the system, that was regarded as just fine. In one hospital there was a superintendent who did not believe mental illness had a surgical or hereditary component, and instead only subscribed to somatic therapies (like psychoanalysis or hydrotherapy). And at some places they had such institutional turnover in terms of medical superintendents that no straightforward policy ever was set.

So you can see how this complicates your question, as compared to states that had more hierarchical mental health systems, or ones with more oversight into the ordering of sterilizations. In the case of California, the end of sterilization came not because of strong local opposition to it, but because they overhauled their mental health system in the 1950s and reduced the amount of local control. By the time that happened, the use of sterilization had gone out of fashion within the broader mental health community (to be replaced with other things that were often hardly more palatable to modern eyes — like lobotomy). So it ended with a bureaucratic whimper rather than some kind of ideological boom. In general the 1950s were a time of great reform in state mental health systems — a deliberate attempt to move from a still-lingering "asylum" model to something more like a "mental institution" (again, for good and for ill, in retrospect).

The only group during the first half of the 20th century that had a strong, organized opposition to compulsory sterilization of this sort was the Catholic Church, whose opposition to any kind of reproduction control is well-known. The broader associations of sterilization with Nazism and oppressive control, to my knowledge, only emerged in the 1960s and 1970s, well after the heyday of compulsory sterilization in the United States. I do not know of any surgeons who opposed it while it was happening, but if any did, I would not be surprised if it was for religious reasons, as opposed to the reasons we would object to it today.

Anyway — this is only a very limited answer (very California specific), with an indication about why I think that many histories of sterilization and eugenics fail (in that they take the shared ideology as a given, when the local practice can be much more complex). I have written this up at some length (published about a decade after I did the research originally) if you are interested, and the footnotes point to the kinds of sources that exist on it: "States of Eugenics: Institutions and Practices of Compulsory Sterilization in California". The referenced Laughlin book (Eugenical Sterilization in the United States, 1922), in particular, has quite a lot of testimony from physicians in it — it is a piece of propaganda, to be sure, but as far as propaganda goes, he does a very good job of outlining how various doctors, lawyers, judges, etc., felt about sterilization, because he was very keen on actually figuring out how to make sterilization happen in an orderly way, and so he took a very clear-eyed approach to the obstacles in his path, if only to overcome them (and was crucial to both setting up the Virginia sterilization law and the Buck v. Bell case that caused SCOTUS to rule it constitutional in 1927).

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