While this statement is true, the major issue here is this can easily become, inadvertently, an argument that really is not dispositive as to what was really happening, en masse, at the time. We need to be careful of reviewing with morally-clouded, rose-colored glasses.
For every institution that man has created, there were always people on both sides. I cannot think of one insitution where there were not dissenters/proponents on one side or another, Therefore, to say that others at the time disagreed with and were questioning Calhoun and slavery is simply stating that different parts of the world and different peoples held different views and acted accordingly. However, was that the overriding, superior morally-held position at that time? It really depends on what you consider as proof of moral superiority.
For example, at that time, dictatorships, imperial rulers, and every form of totalitarianism were the norms, but there were dissenters which developed more freedom-based societies. However, these “free” societies were few, very few, and the dissenters re slavery were concentrated in those societies. If aliens were looking down on Earth at that time, they would think subjugation of people was the accepted practice, and that England was bucking the trend. The alien would easily judge England as strange and out of kilter with the rest of the world, not necessarily holding the morally superior position. In the case of majority rules, aliens could have easily seen England as at the end of line and not following what the rest of the “smart” majority of the world was doing.
My point is the fact that there were people who disagreed with slavery and Calhoun does not indicate or prove that, at the time, the non-slavery position was actually viewed superior. Given the governing evidence, it could be concluded that slavery was considered the more normal and superior of institutions.
In hindsight, yes, we can say that one position was superior to another, but to now use as an argument that people back then disagreed indicates a superior position is not supported by the governing evidence as practiced by the overwhelming majority of countries at that time.