I rather no company patent them than any do-no-evil company. Besides why do you think they won't use/abuse it? The whole point of spending so much ridiculous amount of money on a patent is to get exclusive rights to be the only one to use it. Isn't competition better than stagnation by a single company?
Nope, but that doesn't matter - as enforcement is the concern, and there prior art shines. If the motive is purely defensive (and I don't include the menacing of a portfolio in that category), then it is the ideal move to make - as bad actors waste more energy filing poorly researched and easily refuted patents.
Probably doesn't prevent the granting of a patent, however it makes it impossible to enforce the patent. Mike and I published this in 1998 http://www.rage.net/wireless/wireless-howto.html . A Cisco legal team found this in 2008 and contacted me because the owners of patent #7035281 were coming after them. Doing a simple write-up of what I thought was obvious at the time - stick a wireless card into a Linux PC and have it route packets - may have saved all of us from having the wifi router in everyone's home restricted by patents. So whatever ideas you implement, be sure to blog about them and make sure archive.org gets a copy.
The problem is that other people will just create one or more patents which are around using your breakthrough algorithm in different contexts. The famous amazon one-click shopping patent as an example. The internet is the breakthrough, but because there's no patent on that, its easy to surround with patents that should be too obvious to be patents, but have legal teeth even so.
If you patent the core idea, the other patents become a lot less useful. (Not that I think Google is thinking this way. It's just a PR problem to them. When no one is looking, I bet they do whatever they can to get as much money/power as they can.)
It is a terrible situation, and putting out prior art certainly doesn't fix that - but the alternatives courses of action are worse (assuming purely defensive interests). I think you're right though, if the internet was somehow patented then we wouldn't have one-click shopping patents... or much of anything really - we'd likely be having this discussion over a Minitel service.
Consider the development of Microsoft's attitude regarding software patents. There's no reason whatsoever to think these patents are in good hands with Google, especially considering that their Android licensing policies seem to be carbon copies of old Microsoft tactics.
Their goal as it seems up to this point is to get a monopoly on the framework and technology with opensourcing of their framework. Good for hires and keeping the competition in check. A patent will tighten their grip on ai.