I'm not one who agrees that 2 wrongs make a right.
Jihad was certainly a thing though, but also needs to be put into the context of the historical period where conquest and warfare were commonplace regardless of religious identity.
Isn't the second quote of yours a form of "two wrongs make it right" ?
In any case, I get your point, and while I've already agreed that Spencer has a clear agenda, I don't think his books are extreme. Certainly no more extreme than the common refrain "Islam is a religion of peace".