For example, a typical ISIS member could be described as a militant radical Islamic terrorist and none of that description is redundant,
I'm not sure. Radical seems pretty redundant there, I've never heard of a moderate militant Islamic terrorist.
Eh, there's almost certainly some out there. You don't exactly have to have extremist beliefs to engage in a terrorism campaign, and it's pretty likely there's been a number of folks that were otherwise moderate people that engaged in terrorist attacks against an invading force or particularly despotic government. When you're dealing with an extremely asymmetric force situation it... really is pretty close to the only way to do something approaching significant damage. Or at least acts that are completely indistinguishable from terrorism save an arbitrary relabeling based on target.
There's that, and there's also that "radical" is a modifier of "Islamic" rather than "terrorist", just as "militant" is. Radical in that they espouse extreme fringe views, militant in that they push their perspective aggressively, and terroristic in that their radicalism and militancy are expressed through political violence rather than other channels.
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Take, for example, a member of the WBC. They're radical militant Christians, but they're not terrorists. Their interpretation of Christianity is radical, their support for and expression of it is militant, but they use methods other than terrorism to pursue their goals. Then look at, say, a fairly moderate member of a mainline Protestant denomination. Their views likely aren't radical, their adherence to and propagation of their faith likely isn't particularly militant,
and they don't engage in terrorist acts to support it. Or a member of a Southern Baptist congregation. Their views probably aren't too radical, but there's a good chance that they're much more militant than other Protestants, though they still aren't terrorists unless they're doing stuff like bombing Planned Parenthood clinics.
So both ISIS and the WBC are
collections of massive dickheads radical, militant members of their respective faiths. Incidentally, this is a large part of why (for those of you who wonder why people care more about Muslims being bigoted assholes with Bronze Age ethical values) Islam gets a lot more heat than Christianity or Judaism from agnostics and atheists. Extreme fringe Christianity is generally people being total cunts to other people for no good reason interspersed with rare bits of spontaneous or (even more rarely) planned violence on the individual level. Extreme fringe Judaism is, in addition to the above, the Zionist shitheads conducting ethnic cleansing over in Israel and blocking international action to stop it: relatively few in number, in a small area, and (let's be honest here) not something likely to endanger Western commentators. Extreme fringe Islam is fucking terrorist attacks and beheadings, pedophilia, marital rape, and active sectarian violence.
That's why, as an atheist, I care more about Islam than the other Abrahamic faiths. Because, by and large, the Christians and Jews have been socialized enough by secular civilization that they don't really engage in that sort of barbarism any more. It's mostly in the past, and unless you're in the business of guilt-tripping people for the actions of their ancestors *cough*SJWs*cough*, that's where it stays. The bigotry and dehumanizing occurs predominantly through speech and social interactions: still a damned serious issue, but for the most part people aren't being
literally murdered for having differences of opinion the way they were back in the early 1600s or whatever.