Mark is a convert from evangelicalism, a Catholic apologist, and a writer. (Also a friend of mine. :-))
and why is he so mad at traditional Catholics?
There's a certain subset of traditional Catholics, some of whom are de jure inside the Church (and some of whom aren't), who are more "traditional" than charitable. I would read his remarks as applying to them, not to the vast majority of Catholics who would think of themselves as "traditional Catholics" (of which I am one).
His exaggerations and his comparison of traditionalists to Muslims are highly offensive.
And I'm just a retread Episcopalian with a liking for Latin, not a die-hard traditionalist in any sense of the word. I attend a quite normal (if also quite orthodox) Ordinary Rite parish in a suburb of Atlanta. We throw in a little Latin from time to time and have very traditional music, but this is no nest of sedevacantists.
So if it offends me it's way too strong and he has missed his target completely.