I don’t know what the big deal is. It’s what you believe and your disposition that counts, not whether you take the cup.
This is from the Council of Trent:
CANON I.-If any one denieth, that, in the sacrament of the most holy Eucharist, are contained truly, really, and substantially, the body and blood together with the soul and divinity of our Lord Jesus Christ, and consequently the whole Christ; but saith that He is only therein as in a sign, or in figure, or virtue; let him be anathema.
CANON lI.-If any one saith, that, in the sacred and holy sacrament of the Eucharist, the substance of the bread and wine remains conjointly with the body and blood of our Lord Jesus Christ, and denieth that wonderful and singular conversion of the whole substance of the bread into the Body, and of the whole substance of the wine into the Blood-the species Only of the bread and wine remaining-which conversion indeed the Catholic Church most aptly calls Transubstantiation; let him be anathema.
CANON III.-If any one denieth, that, in the venerable sacrament of the Eucharist, the whole Christ is contained under each species, and under every part of each species, when separated; let him be anathema.
CANON IV.-If any one saith, that, after the consecration is completed, the body and blood of our Lord Jesus Christ are not in the admirable sacrament of the Eucharist, but (are there) only during the use, whilst it is being taken, and not either before or after; and that, in the hosts, or consecrated particles, which are reserved or which remain after communion, the true Body of the Lord remaineth not; let him be anathema.