My anti-catholic relative made a claim that years ago Catholics separated mentally and physically ill people from society believing they were possessed. Is this true?
Whenever someone makes a claim – whether positive or negative – it is his responsibility to prove it. Politely insist that your relative do so. As it is, his claim is so vague that it is impossible to answer, as posed. It is possible that the claim is false. It is also possible that it is somewhat true, but not as presented (e.g., certain countries or societies that are traditionally Catholic may at one point in their histories have done so but it may have been entirely unrelated to the professed religion). Without a concrete claim and substantiation to support it, there is nothing that can be dispassionately examined.