In the context of the time, I think radical is indeed an appropriate word, for the ideas being espoused took a sharp turn from the prevailing wisdom and orthodoxy, that general warrants should be illegal, that men should hold only one office at a time, that there was higher law than acts of Parliament, that those in power should be criticized and even ridiculed, these were truly radical.
my objection isn't to the meaning of the word. Must I exert myself to point out that meanings are meaningless in the age of mass media? It is associations and perceptions that move people. In the popular mind, there is no difference between a Jihadi and a Minuteman (I count 8 of the latter in my lineage) if the hot word of the day is "radicalized".
Freegards.