In essence, "conservatism" then was support for a government that actively favored the rich and powerful, liberalism was support for a neutral government, and socialism was support for a government that actively favored the poor. So a 19th century attack on liberalism -- such as that of this Pope Leo 13th -- would have to be considered quite reactionary by virtually everyone today.
The usurpation in the U.S., by FDR and others around 1930, of the name "liberal" for what is really socialism, was made more tenable given that there basically aren't any longer any people who are conservative in the 19th century sense (actively favoring the rich and powerful). (True conservatism does exist in some countries: for example, I understand that in Pakistan only the poor and middle classes pay taxes; the rich landholding aristocracy pays little or none). Since the socialists slid over to using the term "liberal," and these liberal-socialists controlled the government, media and academy and could thus enforce their use of the language, 19th-century liberals had to take on the name of conservatism or libertarianism.
Rebellion is pandemic in our society; everywhere, people cry out for freedom from Church, State, parents, teachers, or anything else that denies them the satiation of the senses or the deification of the Self. The worship of the goddess Liberty has become our national cult; piety towards our Creator and loyalty towards our ancestors (i.e. traditionalism) have been cast aside by our culture. Confronted with the majesty of God and His Law, we turn instead to the worship of the golden calf of that makes us happy -- our own selves. But there is no happiness there. There is no freedom there. There is only us, enslaved to our nerve endings for all eternity.
The freedom promised by this world is an illusion. Every man who "liberates" himselves from the Yoke of God only chains himself to the millstone of his own desires. The way of Self, as both Our Lord and the Buddha pointed out, is the most abject slavery of all. Only by dying to Self -- by renouncing the illusion of individual liberty and submitting our wills to God -- can we hope to live. In a very real sense, the only way to be free is to become a slave of Christ. "He that loses his life for My sake shall find it."
Only by acknowledging Jesus Christ as our LORD -- not our buddy or our peer but as our absolute Master -- can we ever be free. Christianity is a religion of humilty, not pride; of submission, not of independence. Only by throwing away our pride, by humbling ourselves before God and the authorities he institutes here on Earth (even when it hurts!), and by dedicating ourselves to obedience, order, and our duty can we ever cast of the shackles of unquenchable desire and truly be free.
"Where the Spirit of the LORD is, there is liberty."