Reffering to google :
Radicalism is : the beliefs or actions of people who advocate thorough or complete political or social reform.
We can also define the radicalism as a form of strict installations in the mind. Those are beliefs hard to change. Only if a very poweful proof will be found.
The word may looks like fanaticism but it's not. The fanatic don't care about any new arguments and keep pushing his opinion being aggressive sometimes.
Radicals may look for a better change what make them fight for their ideas. They are sure that it will bring good things in end. But fanatics can be like crazy believing in something without digging deeper. Fanatics are usually brainwashed.
We can be radically fighting for freedom. For the benefit of crowd against a group of people. Especially if that group is clearly harming others. It doesn't mean that we don't spare that group of people, but it means that we fight for the rights of society. We may just want the fair distribution of the resources. And the goal is noble. The goal may justifies the facilities.
We can also say that something is radically beautiful. It doesn't mean that's bad. The world can be used just to make people who fight looks bad. Because most people think that redicalism and fanatism is the same. And for a group of people it's not that beneficial to make people have strong feelings to something. Because if you don't have such strong feelings of love, you will not have a strong feeling of the wrong things done. It's a big manipulation.
You don't have to be afraid of being radical, but you have to fear to make mistakes that will not bring you to success and that not let you reach your goals.