Upvote:-2
It is unlikely that he was right, and it is unlikely that there is any evidence either way, but it is natural that he said that.
People see patterns everywhere, regardless of whether they exist in reality (the "face on the moon" is the canonical example).
held that religious ministers committed a "blasphemy" when they taught [slavery] as sanctioned by religion
IOW, he expected religious people to be anti-slavery, and thus was more sensitive to religious people being pro-slavery (i.e., has was holding them to a higher standard - possibly subconsciously).