Patents are like nukes. The only "defense" they grant is mutually assured destruction. With trolls, there is no other "company" to destroy, as they make nothing but lawsuits. Add this to the fact that the patent office is so screwed up that they're granting patents on the same "technology" over and over again to different applicants and you get:

tl;dr : There's no such thing as a "defensive" patent. Patents don't make peace. They don't even make war. They just make destruction.