The Catholic Church is the caretaker of many treasures of art and architecture, created all over the world by Christians to praise God. These goods are worth money, but they are really priceless, and by being in the hands of the Church who created them, they are available to all. Selling all the goods of the Church, all of which are in the hands of small congregations of Christians and are the patrimony from their ancestors, would bring in some money, of course, but it would take even more money to replace the buildings, and they would have no art to inspire.
The Church does not have much money (the Vatican was in the red recently), and most of what she collects she gives to the poor. She is the largest provider of social services. Henry VIII and Elizabeth had the same idea you did, so they closed down all the monasteries and seized their treasures. As a result, the entire social welfare and hospital system of England was shut down. (The monasteries were the entire social welfare and hospital system of England.) The result was a horrible misery, which lasted through the time of Dickens, who wrote about the mean-spirited non-Christian attitudes of the Protestant society that was excessively individualistic.
In addition, the treasures that were stolen from the Church were handed out to cronies and became the basis for an unjust class system. Usually when people want to despoil the Church to help the poor (when the Church does most of the helping of the poor to begin with), they really just want to despoil the Church.
As for the Vatican Library, it is open. Many items are ancient and delicate, most are in foreign languages, and some, I believe, still need cataloguing. Some things are secret, in the sense of confidential Church records. Suppose you were a king and wrote to a Pope confessing many misdeeds and asking that a Church be built. You would not want your letter to be make public.
I guess to sum up, it is right to say that the Church is the custodian of much great art created for the service and praise of God.
•If this art were in the hands of private individuals, it would not be available for all, or it would be destroyed.
•If it were in the hands of states, it would be seen intermittently, and subject to political turmoil and war.
•It is not liquid wealth, and even if the Church wanted to sell it for the poor, there would be no one who could buy it!!!
It doesn’t cost the Catholic Church a dime to stand up in the “bully pulpit” and renounce queer marriage. Period.