I like Diety's answer about radicalism occuring correllational to the viciousness of backlash to progressiveness. What is "radical" is merely whatever deviates from conservative or religious magical "norms". All progress in history has been due to radicalism. The founding fathers of this nation were called "radicals" the world over because they dared to defy historical "traditional" "natural law" and "divine rule" of monarchy. My first love was a Black man. In those times, Black / White relationships were HIGHLY "radical" and the backlash was vicious. He and I caused no one any harm. But our cars got trashed, we had to hide our relationship and even my own father, a Black Rights activist, expressed displeasure, mostly realistic worry for our safety. Back then, like in the movie "Guess Who's Coming To Dinner?", White people did NOT invite Blacks to their homes for dinner. When my boyfriend came to my house for dinner the first time, a neighbor came over and actually complained, actually laced his words with threats. HE was the sicko, the DANGER to true decency, not us.
If it wasn't for "radicals" like my boyfriend and I who brought change, we'd still be living in that puke of a paradigm. Why is the Conservative/Republican disturbing penchant, for example, for sterilizing poor people and Black people not called "radical"? Why is killing half a million women and children in a Republican / Conservative piggy-fest war for oil not considered "radical"? I define "radical" as pushing the envelop of Social Consciousness. Even the WORST of so-called "radical" feminism, such as SCUM, which wasn't feminism but rather misandry, has been nothing but WORDS. I consider "radical" and "dangerous" and sick to be not that which does harm to the "moralities" of conservative "norms" and precious "way it should be", but that which causes REAL harm to real people. Feminism has secured legal protections for the rights of 50% of the people, the ONLY rise in history of any demographic group into legal protections for their rights WITHOUT violence, war, revolution and tens of thousands of deaths.
It may be "radical" to suggest, say, that women should never marry or should abort male children or other such weirdo nonsense. But, how is that as much a harm or danger or threat to humanity, those WORDS, as say the Republican / Conservative "Abstinence Only" version of sex education imposed on all of us which the CDC now attributes to the 1/4 girls under 18 infected with STDs rate or taking food out of the mouths of children and letting over 136,000 American children starve to death or sterlization programs that were done in the 60's and are being introduced again today in legislations by Republican / Conservatives? Why isn't the hate and misogyny directed at women not considered "radical"? Where is the rational realistic mature decent perspective of what is truly morbid and dangerous and what is not? How come, for every accusation of "radical threat" that is made against Dworkin, dead, or against SCUM, written 40 years ago, has there not been a renouncement by so-called MRA's against Warren Farrell's, MRA "leader", alive and well and currently raking it in with his books, for saying it's a father's "right" to sexually caress and "initiate" his own daughter?