Excluding the terrorism issue, can you recall a time or speech where Trump lambasted legal immigration and the crowd cheered?
No, but I do recall them cheering when he says that he'll ban all (emphasis on ALL) Muslims from coming into America.
Let's assume Dylan is a "Christian extremist" (which makes no sense since there's no passage in the Bible you could even "selectively interpret" to call for killing blacks specifically). When you can find something comparable to ISIS, Al Qaeda, or any other lesser known organized group which is more than happy to repeatedly blow up those of its own race in addition to those "infidels" outside it, you might have a valid parallel.
I'm not saying that Roof is a Christian extremist! You're not following my point.
I'm saying that it makes no sense to call Roof a Christian terrorist. His actions are probably divorced from what the vast majority of people identify as modern Christianity.
Likewise, the actions of ISIS are divorced from what the majority of Muslims identify as Islam. When we call ISIS "radical Islamic terrorists," we're exploiting an association, the implication of which is that elements of Islam are inherently violent. Additionally, it places the blame on Islam for the actions of some of its adherents.
edit: As far as the extremist argument goes, the context makes all the difference between the Muslims and Christians. Muslims who commit atrocities these days often do so in the name of an active and powerful terrorist organization that is a current global threat. As for critics not recognizing Christian extremists as extremists, those subset of people are most likely Christians who do not want to acknowledge that their religion can also spawn hatred. I condemn both, but ignoring the additional ramifications of Muslim terrorism in the name of ISIS is just being dense.
To the emboldened section of your post: this is the point.
They pledge their allegiance to a criminal organization. That they consider themselves members of a religious community should be beside the point in this conversation.
Still, I consider Christian radicalism being brought up as simply a weak derailment. Islam is the most dangerous religion to criticise for a reason.
Islam doesn't deserve to be criticized for the deplorable acts of terrorists. We have to differentiate "religion" from "crime."
I think you and Dak both misinterpreted my reason for bringing up Dylan Roof. I'm not trying to say that we should call him a Christian terrorist. I'm suggesting that our resistance to call Roof a Christian terrorist should be carried over to the discussion on "radical Islamic terror."
It's terrorism, and we should focus on the criminal elements and organization. When people say "Muslim terrorists" it simply amplifies people's paranoia and anxiety around Muslims, which is pointless and unproductive.
EDIT: to give one final example:
There have been numerous criminal acts committed by people obsessed with heavy metal, creating a paranoid reaction against the musical genre (I think we're all familiar with this phenomenon).
Should we call those criminals "radical heavy metal terrorists"?