The problem is those "Protestant" RCs who create division by ascertaining the validity of church teaching by examination of historical teaching (even if Scripture is not the supreme standard, as with true Prots), and thus do not let Rome "interpret" what such really teaches at any given time.
Among other examples of why this is needed for cultic unity:
Council of Constance 1414-18; SESSION 13 - 15 June 1415: In the name of the holy and undivided Trinity, Father and Son and holy Spirit, Amen. Certain people, in some parts of the world, have rashly dared to assert that the christian people ought to receive the holy sacrament of the eucharist under the forms of both bread and wine. They communicate the laity everywhere not only under the form of bread but also under that of wine, and they stubbornly assert that they should communicate even after a meal, or else without the need of a fast...
although this sacrament was received by the faithful under both kinds in the early church, nevertheless later it was received under both kinds only by those confecting it, and by the laity only under the form of bread....To say that the observance of this custom or law is sacrilegious or illicit must be regarded as erroneous. Those who stubbornly assert the opposite of the aforesaid are to be confined as heretics and severely punished by the local bishops or their officials or the inquisitors of heresy in the kingdoms or provinces in which anything is attempted or presumed against this decree, according to the canonical and legitimate sanctions that have been wisely established in favour of the catholic faith against heretics and their supporters.
...when the one bread is broken, the unity of the faithful is expressed and through Communion they "receive from the one bread the Lord's Body and from the one chalice the Lord's Blood in the same way that the Apostles received them from the hands of Christ himself. (USCCP: "Norms for the Distribution and Reception of Holy Communion")
Edit: Last quote is from the USCCB - United States Conference of Catholic Bishops - regarding the option of the distribution of Holy Communion under both kinds in the ordinary form of the Mass, which usage has become a daily occurrence in many countries.