Even bogus patents are valuable from a legal POV. The cost of defending oneself from a bogus patent is the same as the cost of defending oneself from a valid patent, and that cost is very high, in the millions of dollars and years of wasted time.

Patents are being used as blackmail or a protection racket on the offense and as a MAD on defense. They are effective at both simply because the cost of litigation to defend against or invalidate even bogus patents is insanely high.

This is what makes patent trolls so frustrating. There is no MAD defense since they make nothing, and thus have no exposure to countersuits. On the other hand, the cost of settling is an order of magnitude less than the cost of defeating against them, bogus or not, so the logical response is to "roll over" and pay the license fee. Unfortunately, that just encourages them.