It's loathsome because she blamed masculinity for mass shootings. How exactly is that any different from blaming Islam for terrorism?
As far as I know, most terrorists are not Muslim. Though I would love decent statistics on that; most of the ones I see are about America, where there aren't that many Muslims to be doing the terrorism in the first place.
Either way, you seem to have me confused with an entirely different sort of leftist. I'm an antitheist. I have no problem with considering religion as a factor in terrorism; though I would argue it's not really the most relevant one, I certainly wouldn't call someone using that argument loathsome, in the context of a discussion of Islamic terrorism. Wrong, but not loathsome.
It's also loathsome because she was using it to push her agenda and plug a book.
So she saw a problem, talked about what she thought the cause was, and recommended some reading on the subject. Villainous!
Is that going to be tinted by her political agenda? Obviously. People's politics tend to be related to the way they see the world; if you think gender roles are destructive and dangerous, then you're going to have politics that reflect that.