"All power in heaven and on earth has been given to me. Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, until the end of the age." (Mt 28:18-20)
It is clear that Christ intended that the Bishops (the Apostles and their successors) had the authority and duty to teach the faithful. This teaching authority is called the Magisterium.
The essential point is that there is absolute Truth, which has been revealed to the Apostles, and which they must teach to the faithful. Therefore, all the bishops, and each bishop, when they are in communion with Rome have the power and duty to teach the Truths of the faith to the flock.
Note that Christ said go forth and teach them to observe what I have commanded you. He did not say, go forth and take a poll to see what everyone wants to do and then let them do it. The Pope and Bishops throughout the history of the Church have taken very seriously the onerous duty of preserving the Deposit of Faith and teaching it to the flock entrusted to them. Dissent from Church teaching (even Church teaching that has not been infallibly declared) is essentially an indication by the dissenter that they understand better what Christ commanded the Apostles than the Bishops to whom Christ promised that knowledge.