I agree with greg here. "Republican" in the US and in Ireland mean different things. Both, theoretically, mean "advocates of a Republic." But in political usage, words shift around in meaning.

A scientist is someone who thinks scientifically. To think scientistically has a different connotation, and has no bearing on whether one is a scientist.

To be a scientist and a Christian is not to be a Christian Scientist.

To be human is one thing, to be a humanist another.

To be Islamic is one thing, to be Islamist another.

Let's put it this way: plenty of people on this list make this distinction: "I'm not an anti-Semite. I'm just against Zionism."

"Islamism" is like the Islamic version of Zionism, but on steroids.