Liberalism as defined by wiki:
From the Latin liberalis, "of freedom" is the belief in the importance of liberty and equal rights.Liberals espouse a wide array of views depending on their understanding of these principles, but most liberals support such fundamental ideas as constitutions, liberal democracy, free and fair elections, human rights, free trade, secular society, and the market economy. These ideas are often accepted even among political groups that do not openly profess a liberal ideological orientation. Liberalism encompasses several intellectual trends and traditions, but the dominant variants are classical liberalism, which became popular in the 18th century, and social liberalism, which became popular in the 20th century.
When I read the definition above, I think of concepts that are usually associated with the founding of America such as laissez-faire and separation of church and state, possibly a close definition of modern-day libertarianism
John Stossel
...By contrast, libertarians want government to leave people alone—in both the economic and personal spheres. Leave us free to pursue our hopes and dreams, as long as we don't hurt anybody else.
Ironically, that used to be called "liberal," which has the same root as "liberty." Several hundred years ago, liberalism was a reaction against the stifling rules imposed by aristocracy and established religion.
I wish I could call myself "liberal" now. But the word has been turned on its head. It now means health police, high taxes, speech codes, and so forth.
So I can't call myself a "liberal." I'm stuck with "libertarian." If you have a better word, please let me know....
A typical reaction to libertarianism
Another point is referencing the Constitution