This only works if the patent troll believes the patent can be invalidated. This is rather hard for many patents - a lot of the time patent trolls own legitimat

This only works if the patent troll believes the patent can be invalidated. This is rather hard for many patents - a lot of the time patent trolls own legitimate patents, they just try to apply them over-broadly. You would defeat them in court, but would not automatically invalidate their patent - you may only be able to show that their claims do not cover your work.