“There is something so unaccountably shameful in the nakedness of man,” he says, “that scarcely anyone dares to look upon himself, even when no witness is present.”
This is an interesting passage, if it's the one you're thinking of. What Calvin is not saying is that looking at women causes him lust and "sin." It seems to me his primary conflict is against looking at the male body—his own! He is experiencing some kind of revulsion or shame at seeing himself.
So in the annals of gay panic this is not particularly out of place. I didn't want to get too provocative, but it even reminded me of how transgender people have discussed looking at their gendered bodies with disbelief or disgust.