I would have suggested that "Islamist" was one who proposed the Islamic takeover of the world and the imposition of Islamic rule and law on all.

The religious nutter now dead in Toulouse went, I think, even further.

And I should perhaps draw another distinction, namely that he alleged he was acting on behalf of certain groups, but as far as I am aware they have not yet claimed him as one of their own.

I would also add that it seems that professed Muslims are disproportionately represented in recent times in atrocities - albeit in some cases in response to what could be seen as attacks on their culture or beliefs: but before them (to list just a few) it was the Irish, the Algerians, "freedom fighters" in Malaya, the Catholic establishment against heresy, and mainstream Crusaders - oh and Romans against Christians and Jews.