"The term Radical (from the Latin radix meaning root), during the late 18th and early 19th centuries, identified proponents of democratic reform, in what subsequently became the parliamentary Radical Movement."

"The term political radicalism (in political science known as radicalism) denotes political principles focused on altering social structures through revolutionary or other means and changing value systems in fundamental ways. "

And of course the classic Rules for Radicals book about community organizing and starting grassroots movements.

Let's not label all radical things bad, it can become a way to suppress dissent and societal change.