Writing about nothing but Islam in itself sounds quite a reasonable specialism. That's a pretty sizeable sort of specialism.
It's like saying of someone who writes a book about some aspect of America that they must be a bit suspoect since all they seem to write about is America. Even more so, because America is a much more restricted and localised specialism.
"Borders" I take it is a book shop. I think the most I would take away from dipping into a book in a bookshop in the way of literary criticism would be "No, I don't think I want to buy that one - and I don't think I'll bother to look for it in the library."
Incidentally that link to the non-Taleban Seekers in my last post didn't come through - here it is, with a musical soundtrack. We need cheering up in these times. (You know, leaving aside that Judith Durham is a woman, they sound remarkably like Coopes Boyes and Simpson...)