You are incorrect. Pope Leo III forbade the liturgical use of the filioque in the creed and even had a silver plaque placed in Old St. Peter's in Rome without the filioque. But the Franks ignored the Pope and continued using it.
The Catholic Encyclopedia's author is trying to gloss over this fact of history. The Church of Rome OMITTED the filioque.
From the USCCB website: While Leo III affirmed the orthodoxy of the term Filioque, and approved its use in catechesis and personal professions of faith, he explicitly disapproved its inclusion in the text of the Creed of 381, since the Fathers of that Council - who were, he observes, no less inspired by the Holy Spirit than the bishops who had gathered at Aachen - had chosen not to include it. Pope Leo stipulated that the use of the Creed in the celebration of the Eucharist was permissible, but not required, and urged that in the interest of preventing scandal it would be better if the Carolingian court refrained from including it in the liturgy. Around this time, according to the Liber Pontificalis, the Pope had two heavy silver shields made and displayed in St. Peters, containing the original text of the Creed of 381 in both Greek and Latin. Despite his directives and this symbolic action, however, the Carolingians continued to use the Creed with the Filioque during the Eucharist in their own dioceses.
The controversy has a lot to do with the imprecision of the Latin verb precedere, which means to send. It stands in stark contrast with the meaning of the original Greek text that uses ex pouresis, which connotes an origin of the Holy Spirit from the Father alone.
Pope Francis should consider striking the filioque from the Latin creed as a gesture to the Eastern Churches.
The Vatican's Pontifical Council for Promoting Christian Unity put out an excellent document on the subject back in the 1990s. www.ewtn.com