Reason is ordered to the truth, just as faith is. Consequently when we indolently do not seek the truth, or when we willfully ignore it, or when we refuse to believe it, we abuse reason and sin gravely by virtue of the fact that we have deliberately overthrown the purpose for which God gave us reason in the first place. Consequently Pope John Paul II writes, in Fides et Ratio §25:
Although each individual has a right to be respected in his own journey in search of the truth, there exists a prior moral obligation, and a grave one at that, to seek the truth and to adhere to it once it is known. [quoting Veritatis Splendor §34]
We do not have the right to believe whatever we want, and we do not have the right to abuse reason so as to “justify” our opinions in whatever way that we wish. Freedom is not license.