Roman Catholics certainly believe they are cannibals - although none would admit to it.
Through
transubstantiation they believe that the bread and wine of communion actually becomes the body and blood of Jesus.
Thus, if they believe this, they must accept that they are cannibals.
Whether they are such in the eyes of others, who merely see them digest bread and wine, is a different matter. Certainly a court of law would not convict them as such, if consentual cannibalism were a crime (not sure if it is or not).
Likewise, if someone truly believed they were a murderer - but had done nothing wrong.
Unfortunately the only way you get this conflicting view between self and society is if one party is delusional.
And of course, the RC family would claim that the body and blood of Jesus is no longer human flesh and blood but food of a higher plane and thus would not constitute cannibalism blah blah blah.
So in answer - the RC folk would come up with a reason not to think of themselves as cannibals, although they "believe" they are eating the body and blood of a human that died a mere 2,000 years ago - so presumably fairly rancid and putrid as well?