Unlike trademarks, you can hold a patent without having to defend it. You are not legally required to use it. So the choice to use it is yours. The logic behind defensive patents is similar to creating nuclear weapons as a deterrent and the theory of mutually assured destruction.
Except the superpowers with all the nukes routinely fling them at each other. Where is the deterrence?
If IBM is not deterred by Microsoft's patents, why would they be deterred by mine?
I think you're mistaken about superpowers flinging nukes at each other. Only two nuclear weapons have ever been used in war, and that was 65 years ago.
It was analogy / metaphor.
All the superpowers == all the big companies (Google, Apple, Samsung, etc)
routinely fling nukes == lots of patent litigation.
Good call. That interpretation seems obvious in retrospect.
If you patent an invention, no one else can. Your patent prevents other people from patenting the thing that you depend on.
If your next question is that the existence of your invention would invalidate their patent due to prior art, that would take costly legal maneuvering to establish. Is there a shortcut around that legal maneuvering? Yes, patent your invention first.
I mean, the whole point of a patent is to be able to sue people who are competing with you. How can that ever be defensive?