Just publish all your findings and establish prior art and you should be ok. Or is there more to it?

How can you guarantee that the person publishing their findings won't change their mind later and apply for a patent?

In the US they have one year to file. In UK, EU, and most other countries public disclosure bars them from filing a patent application.

But there is no way to really be sure. Because they may have filed something before or after (within the 1 year) public disclosure.

Is there a way to waive that right?

Indeed, that could do it I think.

That isn't exactly how defensive patents work. Part of the deal is to build up a portfolio you can counter sue with and then force a patent sharing agreement where the two parties agree not to sue either either for any patents.

Its just a mutually assured destruction arms race. The system is broken.

How would that work? If company A receives a "defensive" patent on a technology design, and company B decides to use that patented design without a license, seems like they'd be able to without any recourse. In which case, does the patent system even make sense anymore? I think that's the bigger question in the context of software.

That's the point. The idea of having a "defensive patent" is to avoid having trolls patenting the same thing and then going after small companies with no means to defend themselves in a patent suit. For instance: https://www.x-plane.com/2015/12/patent-troll-update/.

Anyone would be free to use the patent. But trolls can't sue with it.

The way the system is supposed to work is that simply publishing should be sufficient to prevent anyone else from registering future patents on anything that you've published. After all, publishing creates prior art which should invalidate any future patents covering your technology.

Defensive patents are for when IBM comes after you with a stack of patents demanding licensing fees amounting to 3% of your revenue.

Then you whip out your defensive patents and demand that IBM licenses your IP for 3% of their revenue. (Win-win cross licensing ensues...)

Patent trolls are a different animal though. However, having some good patents may at least protect you from willful infringement (increased damages)

I feel like this is just a loose-loose situation that instead of encouraging and protecting small innovators from the power of established companies instead just locks them out. Patents are essentially MAD (except of course for the part where everyone dies if it goes wrong). Like nukes, these patents aren't actually useful. They are only necessary because everyone else has them and the people actually under threat are the less powerful people that don't. This is very different from say pharma patents, where companies seem to directly benefit from Patents in their intended way.

I wonder if it's time for a Patent Denuclearization... but I'm not exactly sure how that could look like.

theoretically publishing an explanation of the methods and not patenting it is sufficient

Not since the US changed to first-to-file. A patent can be issued to another party and you can be sued for using your own invention. If an examiner never finds your prior art you're still on the hook to deal with the expensive legal process of defense and invalidation.

Elsewhere prior use is an absolute defence against being sued for patent infringement; I've not seen USA caselaw on this specific issue but I can't see how it could be different.

Prior use in public would count as "prior art" and void a patent too.

I don't think first to file is relevant to prior art ( direct from attorneys for things I've tried to patent this year with medical devices)