A Zen master is a Buddhist fundamentalist. Zen masters, such as the late Shunryu Suzuki, shown in the picture here, try to practice Buddhism in its pure form. They try to do things the way Buddha did them, and they try to follow Buddha's teachings. They live austere lives devoted to meditation and teaching, just like Buddha did. They try to focus more on direct experience than in learning doctrines (something Buddha repeatedly stressed in his teachings). They try not to conceptualize too much. They get their students to learn about their own minds from long periods of meditation.
A Buddhist fundamentalist cultivates a state of calmness and kindness, and cultivates the ability to keep her or his attention in in the present moment and not in the past, the future, or lost in thought.
These are Buddhist fundamentalists.
If Zen devotees work hard, most of them will achieve a state of abiding inner peace and a profound and lasting feeling of kindness toward others.
Islamic fundamentalists try to practice Islam in its pure form. They try to do things the way Mohammad did them, and they try to follow Mohammad's teachings. They live austere lives devoted to jihad. They don't sit around contemplating their navels. They prove their devotion with action. They try to make the law of Allah the supreme law of the world. They devote their lives to fulfilling the political goal of Islam, just as Mohammad dedicated his life to it, and just as Mohammad taught his followers to do.
An Islamic fundamentalist cultivates hatred toward non-Muslims and works toward the day when all non-Muslims are either subjugated as dhimmis, converted to Islam, or dead.
These are Islamic fundamentalists.
If Islamic devotees work hard, most of them will find themselves in some form of warfare with non-Muslims and ideally will be killed fighting in the way of Allah.
Are all fundamentalists dangerous? Are all ideologies the same? Would it matter to you what kind of fundamentalist you had as your neighbor? Would it matter to you what kind of fundamentalist your children chose as close friends or heroes? Would it matter to you what kind of fundamentalist your country allowed to immigrate to your country?