Radicalism isn't a right or left thing, it's both. Folks who want to drown government in a bath tub exist on both sides of the political spectrum. People who want freedom without consequences are as prevalent on the right as they are on the left. What we can learn from radicals , left and right, is that their formerly extreme views often become our eventual mainstream ones. Consider how radical "gunowner rights" have been and how they have been mainstreamed by the NRA and other 2nd Amendment proponents. Consider how Marriage Equality and Don't Ask, Don't Tell are moving more and more to the mainstream thanks to the left.
What we should learn from radicals on the left and right is that these movements don't take place over night and the mainstream tends to gravitate in gradual steps. This is why it is important to view the left or right leanings of the nation as a harbinger of things to come. And often the leanings take place in the halls of government.
The changes that have been played out in placing individuals on the Supreme Court is, in my opinion, the most important application of radicalism: putting people with radical ideas in the places of power. As a result of neoconservative radicalism, we have given rise to rampant corporate power-grabbing, lessened civil liberties to give government more power, and awarded more personal power to those who would enact it by the business end of a gun.
Radicals teach us that nothing can be gained without struggle. They teach us that without moderating forces, the values we presume to be our birthright are not protected. They teach us that we must be in the fray or willing to accept the consequences. Most importantly, they teach us that if their ideas are championed in the correct places, cooler heads seldom prevail.