Barring Kerry from Communion is for the protection of his own soul.
The doctrine of transubstantiation exists in the Catholic Church. For sure the faithful hold that the eucharist becomes the flesh of Jesus and wine becomes his blood. Martin Luther rejected that notion, suggesting that the wine and the eucharist merely represent the body and blood of Jesus.
As Kerry took communion in a place other than a Catholic Church, the representation of the eucharist wasn't the same by the offerer. Does one's faith alone cause transubstantiation, or is it effected by the priest? If it is the latter, then a case could be made that Kerry really never received Catholic communion, and his soul is in no danger.