ist is appropriate
Reader comment on item: Islamist Group Tries to Kill Use of "Islamist"

I think the use of ist is appropriate

From Wiktionary

Suffix

-ist

1. added to words to form nouns denoting: One who follows a principle or system of belief.

Marxist, diest

Note, these are relate to -ism, e.g. Marxism, deism

2. A member of a profession or one interested something.

botanist, psychiatrist, one who studies psychiatry

3. a person who uses something.

violinist, one who plays a violin

4. A person who holds biased views.

sexist, racist

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