It is common among Catholics to hear the expression "Let us be charitable with him," used in the sense that one should tolerate the errors or morally bad behavior of someone else. Thus, charity is being used today to cover for almost everyhting wrong we witness, and to set aside habitual Catholic militancy and intransigence.
To counter this liberal approach already present in his time, St. Pius X left the precious teaching below, which can be found in his Encyclical Our Apostolic Mandate written against the modernist errors of the Sillon movement.
EXTREMELY RARE FOOTAGE OF POPE PIUS X WALKING IN THE VATICAN
While He called to himself those who toiled and suffered in order to comfort them, it was not to preach to them the zeal of a chimerical equality. While He lifted up the lowly, it was not to inspire them with a sentiment of a dignity independent from, and rebellious against, the duty of obedience. While His heart overflowed with gentleness for the souls of good will, He could equally arm himself with holy indignation against the profaners of the House of God, against the wretched men who scandalized the little ones, against the authorities who crush the people with the weight of heavy burdens without lifting a finger to alleviate them.
He was as strong as He was gentle. He reproved, threatened and chastised, knowing - and teaching us - that fear is the beginning of wisdom, and that it is sometimes expedient to cut off an offending limb to save the body.
Finally, He did not announce for future society the reign of an ideal happiness from which suffering would be banished; but, by His lessons and by His example, He traced the path of the happiness possible on earth and of the perfect happiness in Heaven: the royal way of the Cross. These are teachings that it would be wrong to apply only to one's individual life in order to win eternal salvation; these are eminently social teachings, and they show in Our Lord Jesus Christ something quite different from an inconsistent and ineffective humanitarianism.
(St. Pius X, Encyclical Notre Charge Apostolique , August 15, 1910