Objection & response

Is indirect communion the same as direct communion?

If communion with the heretic defiles, what of communion with those who commune with him, and where does the chain stop?

The objection, at its strongest

Extending defilement past the heretic himself to everyone who communes with him, and to those who commune with them, is a chain without end. Taken seriously it would unchurch the world; therefore the whole principle must be wrong.

Why it is raised

The communicating vessels logic really does look limitless, and rigorists have in fact ridden it into ever smaller and mutually anathematizing fragments.

Evidence for the objection

The absurdity of infinite regress is a genuine reductio; no Father unchurches the third and fourth link mechanically.
St Theodore himself applied graduated economy, different strictness toward heretical ordainers, concelebrants, and mere communicants, not one undifferentiated sentence.

Evidence against it

The principle itself is canonical, not invented: Apostolic Canons 10 and 11 attach consequences to communion with the excommunicated and deposed, the chain's first link is real.
St Theodore's letters treat knowing communion with the commemorators of heresy as sharing the defilement, the second link is real too, where knowledge is present.
But the tradition bounds the chain by exactly two things: knowledge and publicity. Defilement attaches to knowing consent to open heresy, not to geography, and not automatically to the ignorant, the coerced, or the remote.

A limited conclusion

Strongly supported

Direct and knowing indirect communion share the principle; the chain is bounded by knowledge, publicity, and pastoral economy, on the model of St Theodore's gradations, real enough to make the second link matter, bounded enough never to unchurch the unknowing. Mechanical extension past knowledge is the zealot error; denial of the first link is the indifferent one.