If a radical group were to assume a governing authority, then yes, it can work to a degree. I think that when radicalism is able to voice its opinion with some authority, then people will be more likely to support it and believe in it. I just think it's a dangerous thing.
Radicalism does not work when it assumes government authority. Consider first that if you examine a society, there will be a spectrum of political beliefs. Overall, you will find that political beliefs are split evenly so that one belief is not overwhelmingly popular. If you promote radicalism in a governing authority, then you will only appeal to a small fraction of the population. You will lose support of the other spectrum and of the people who are not inclined to radicalism. Thus, by implementing radicalism, a governing authority will diminish in power and influence.
No, radicalism does not ever work when it assumes governing authority, because radicals oppress people when they are in charge. Radicals do not care how much they hurt people. Usually, it results in mass torture and death. It has in Egypt in the Arab Spring, and it caused death in World War II as well.
Truly radical regimes cannot govern by consent as radicalism is almost never reflective of public sentiments. Radicals may gain office through various means, but soon occupy their time prosecuting and silencing dissent by branding it as "obstacles" and "status-quo". However, the full time prosecution of such agendas inevitably leads to totalitarian regime, police states, and failed visions.
NO, if you look back at all of the radicals in history, they did not ever get their ideas to take over and be the main thing in a system. i think that it would be a lot better if they had a way to not be so radical and be sensible.