Socialism is the opposite as it entails (Among other things) the idea of fast changes, if need be with revolution. Neither does utilitarianism talk about social progress through reform.
Libertarians talk exactly about what the question is about; one of the main tennets of liberalism is that they prefer and would like to witness social change through reforms.
It would be the political orientation of "pragmatism," that favors social progress by reform and by changing laws rather than by revolution, since this holds that most people want to obey laws.
"A desire to reform the U.S. also arose out of the Second Great Awakening. The U.S. temperance and abolitionist movements were both greatly influenced by the revival movement and its messages. Additionally, women's involvement in the revival provided support for the women's rights movement."
There are several elements to this tradition. Freedom of speech, a democracy system where not just one person rule and makes decisions, and a jury system.
