There is so much twisted reasoning in this article that, rather than refute it, it’s easier to post a link to an another source that demolishes ThinkProg’s excuse making for Islamic terrorism: https://areomagazine.com/2017/05/28/no-youre-not-more-likely-to-be-killed-by-a-right-wing-extremist-than-an-islamic-terrorist/
As to amount of coverage: ISIS supporters who kill 14 people at a Christmas party just naturally garner more attention than a random crazy guy who stabs two people on a bus.
And remember, all these terrorist apologists start the death count on the day AFTER the most devastating terror attack in history.
Whether or not you want to call Dylann Roof a terrorist, he was one lone guy who decided to kill a bunch of people because of race. But, unlike the Orlando shooter, or the San Bernardino shooters, or the Chattanooga shooters, etc. was not a devotee of a political/religious movement that has declared war on the US, on Christianity, and on Western civilization.