Which is a clause that can easily be used to justify anything. But looking at history we see much stricter prohibitions.
We furthermore forbid any lay person to engage in dispute, either private or public, concerning the Catholic Faith. Whosoever shall act contrary to this decree, let him be bound in the fetters of excommunication. — Pope Alexander IV (1254-1261) in “Sextus Decretalium”, Lib. V, c. ii:Catholic Encyclopedia, http://oce.catholic.com/index.php?title=Religious_Discussions
Commenting on this, the 1914 Catholic Encyclopedia states, “This law, like all penal laws, must be very narrowly construed. The terms Catholic Faith and dispute have a technical signification. The former term refers to questions purely theological; the latter to disputations more or less formal, and engrossing the attention of the public....But when there is a question of dogmatic or moral theology, every intelligent layman will concede the propriety of leaving the exposition and defense of it to the clergy. - www.newadvent.org/cathen/05034a.htm
But the clergy are not free to engage in public disputes on religion without due authorization. In the Collectanea S. Cong. de Prop. Fide" (p. 102, n. 294) we find the following decree, issued 8 March, 1625: "The Sacred Congregation has ordered that public discussions shall not be held with heretics, because for the most part, either owing to their loquacity or audacity or to the applause of the audience, error prevails and the truth is crushed. But should it happen that such a discussion is unavoidable, notice must first be given to the S. Congregation, which, after weighing the circumstances of time and persons, will prescribe in detail what is to be done. The Sacred Congregation enforced this decree with such vigour, that the custom of holding public disputes with heretics wellnigh fell into desuetude.
That this legislation is still in force appears from the letter addressed to the bishops of Italy by Cardinal Rampolla in the name of the Cong. for Ecclesiastical Affairs (27 Jan., 1902) in which it is declared that discussions with Socialists are subject to the decrees of the Holy See regarding public disputes with heretics; and, in accordance with the decree of Propaganda, 7 Feb., 1645, such public disputations are not to be permitted unless there is hope of producing greater good and unless the conditions prescribed by theologians are fulfilled. The Holy See, it is added, considering that these discussions often produce no result at all or even result in harm, has frequently forbidden them and ordered ecclesiastical superiors to prevent them; where this cannot be done, care must be taken that the discussions are not held without the authorization of the Apostolic See; and that only those who are well qualified to secure the triumph of Christian truth shall take part therein. It is evident, then, that no Catholic priest is ever permitted to become the aggressor or to issue a challenge to such a debate.
“...the Church forbids the faithful to communicate with those unbelievers who have forsaken the faith they once received, either by corrupting the faith, as heretics, or by entirely renouncing the faith, as apostates, because the Church pronounces sentence of excommunication on both.” St. Thomas Aquinas, Summa Theologica, Article 9, “Whether it is lawful to communicate with unbelievers?”; http://www.newadvent.org/summa/3010.htm
“On the other hand, there are unbelievers who at some time have accepted the faith, and professed it, such as heretics and all apostates: such should be submitted even to bodily compulsion, that they may fulfil what they have promised, and hold what they, at one time, received.” St. Thomas Aquinas, Summa Theologica, Article 8. “Whether unbelievers ought to be compelled to the faith?”
Innocent’s Bull Ad Extirpanda prescribes that captured heretics, being "murderers of souls as well as robbers of God’s sacraments and of the Christian faith, . . . are to be coerced – as are thieves and bandits – into confessing their errors and accusing others, although one must stop short of danger to life or limb." — Bull Ad Extirpanda (Bullarium Romanorum Pontificum, vol. 3 [Turin: Franco, Fory & Dalmazzo, 1858], Lex 25, p. 556a.) The bull conceded to the State a portion of the property to be confiscated from convicted heretics. The State in return assumed the burden of carrying out the penalty, and was to be "admonished and induced and if necessary compelled by ecclesiastical censure" "to the best of their ability to exterminate in the territories subject to their jurisdiction all heretics pointed out by the Church... "— Bull Ad Extirpanda (Bullarium Romanorum Pontificum, vol. 3 [Turin: Franco, Fory & Dalmazzo, 1858], Lex 25, p. 556a. Canons of the Ecumenical Fourth Lateran Council, 1215, http://www.fordham.edu/halsall/basis/lateran4.asp)
Is it permitted for Christians to be present at, or to take part in, conventions, gatherings, meetings, or societies of non-Catholics which aim to associate together under a single agreement everyone who, in any way, lays claim to the name of Christian? In the negative! - (Pope Pius XI, Mortalium Animos)
How does a Catholic sin against faith? A Catholic sins against Faith by Apostasy, heresy, indifferentism and by taking part in non-Catholic worship." (Catechism of the Council of Trent, and the Baltimore Catechism)
"If any ecclesiastic or layman shall go into the synagogue of the Jews or to the meeting houses of the heretics to join in prayer with them, let them be deposed and deprived of communion. If any Bishops or Priest or Deacon shall join in prayer with heretics, let him be suspended from Communion" - III Council of Constantinople.
Quinisext Ecumenical Council, Canon 64: It does not befit a layman to dispute or teach publicly, thus claiming for himself authority to teach, but he should yield to the order appointed by the Lord, and to open his ears to those who have received the grace to teach, and be taught by them divine things; for in one Church God has made "different members," according to the word of the Apostle... But if any one be found weakening [disobeying] the present canon, he is to be cut off for forty days. — http://www.newadvent.org/fathers/3814.htm
But that was the past, and doing something or not doing something that would excommunicate a RC in one century can be sanctioned in another, and having lost her unscriptural ability to control media, Rome came to encourage Bible reading, while the "just and reasonable cause" clause that allows the RC faithful to write "for newspapers, magazines, or periodicals which are accustomed to attack openly the Catholic religion or good morals," is interpreted to sanction debate with "anti-Catholics," contrary to times past, though the wording does not go that far, but evidently has writing letters and stories in mind.