eden, radicalism only has a bad name because at the moment it is associated with ISIS.
I don't agree. Radicalism isn't new. Basically it means "change at the root" and, when associated with politics, it has been expressed by means of revolutions. Revolutions are violent movements. In the religious arena, "radicalism" is usually associated with attempts from one group to impose their theological ideas on others, either by aggressive proselitism, forced conversion, or outright violence, and death. ISIS is just the most recent incarnation, but "radicalism" in the realm of ideas is also not new.
To me, Jehovah's Witnesses are a borderline radical christian cult, because they proactively engage in proselytization (although I can't say "aggressively") and they advocate the conversion of the entire mankind to jehovism by means of a massive genocide at Armaggedon.
If an advocate for atheism [or insert any other -ism that you can think of] aims to aggressively uproot theism from their audience, to change the other person at the root of their belief system, even if that attempt isn't welcome, doesn't that qualify as "radical"? That was the use I gave to "radicalism" before.
Eden