Employers and investors who have a problem with this are going to have to weigh the cost of these restrictions against the cost of turning away high-value engineers who can afford to be selective about where they work.
During the hiring process, lots of employers are already giving candidates verbal assurances that their patents will only be enforced defensively. Now, software engineers have a practical way to demand that they make these assurances binding. Employers who fail to do so will have a much tougher time explaining themselves.
I'm probably going to start requiring this of any employers that I work for in the future.
But for hardware or biotech startups? Licensing patents is oftentimes a startup's business model. And licensing doesn't work if people can use technology without paying (which would be the case with a purely defensive patent).
I'd say defensive patents are pretty useless for a startup. The idea is to build a patent portfolio that's so large and diverse that the day some random company sues you, you just happen to have a patent that they themselves are infringing on. You also need the financial resources to pull off that counter threat. Doesn't sound like lean startup to me...
A much cheaper defensive measure is to publish your "inventions". There are companies that help you with that, e.g. ip.com.
It's a balance between the benefit of the recruiting/retention edge for making a commitment to your engineering team, vs. the loss in patent value for an acquisition or to stop someone who's really ripping you off later (the latter obviously being a huge gray area).
They can sue, they just need the inventor's permission. In that case, if the inventor is getting their hard work ripped off, they would probably agree to sue.
No seriously, if I have a startup that cares about my employees, is there any real reason to not do this?