Presumably with the exception of counter-suing companies that have sued you? Companies build patent portfolios so that other companies will be wary of suing them for fear of being counter-sued (simplification). If being a member of this pool removed your ability to even act defensively, I don't think it would achieve its goals.
Exactly. Joining the pool effectively signs away your rights to make offensive lawsuits, in exchange for gaining the rights of the entire pool for defensive purposes.
You're right about patent trolls, but this would allow those companies to have access to a vast amount of patents, so it should become harder for patent trolls to sue any of them, although far from impossible.
But the patent pool would be mostly so those companies don't sue each other. So many companies in the tech industry are suing each other right now. It's ridiculous.
