Originally vaccination was opposed by certain clergymen on the grounds of theological objection to its use. At the present time most of such objection has ceased, It is still clergymen, however, who are the most prominent among the anti-vaccinationists, though now they usually find biological and pathological, instead of theological reasons. They proclaim it a crime against nature, from the biological standpoint, that the disease of an animal should be conveyed to man, even for protective purposes. At the present time one can find just as bitter objections to vaccination in anti-vaccination journals as when the subject was first brought under discussion. Men must find some reason for their opposition, and they take the weapon that is handiest and that they are able to use with best effect. In an era when theological ideas were dominant, theology was ready at hand for this purpose, but any other ology will do just as well, and the history of science, even in the present day, will show that always some ology, regardless of human feelings, is used quite as ruthlessly and as cruelly as in the olden days. There are tortures of spirit that are worse than prison or even fire.
James J. Walsh, The Popes and Science (1908)