IAAPL (I am a patent lawyer), but I am at the very beginning of my career. Anyway, non-lawyers often are too credulous when they get nastygrams from the other side. Don't believe everything they say to you! It's amazing what non-lawyers will believe and do just because they get a mean-sounding email.
That being said, one of the fundamentally unfair things about the legal system is how expensive trials are. Even if the other side here has no case, they might be able to haul you into court and run up expenses for you. Maybe you can become a cause celebre of the anti-software patent blogosphere?