The issue is virality, i.e. derivative work of the AGPL software should also be AGPL, so it's unlikely that serious companies would be willing to take the risk of potentially exposing their entire non-auth stack to AGPL and having to argue the line for what would be derivative work and what is not.
Many big companies have blanket policies either banning AGPL completely, or require strict legal review.
Re the payment question: it is a common SaaS licensing model to dual license under AGPL and a commercial license. AGPL serves as a deterrent for business customers to use it without purchasing the commercial license.
Yes, the use of AGPL as part of the stack certainly raises concerns. I don't think it would apply in this case, but equally I am not a lawyer, and i don't want to pay lawyers to fight over it, so personally I don't use AGPL in my stack, validating your point.
That's right. As long as you give back the source-code of any changes you make, you can self-host Stack. However, modifying without giving back is not allowed under AGPL, so companies that want to do that would need a commercial license. (Though we don't offer commercial licenses or anything like that right now.)
I know it's a subtle distinction, but I'd suggest avoiding the term "give back".
The AGPL requires that source code be supplied to users of the system. In other words "code flows down-stream". There us no requirement to flow the code "upstream".
Now sure, you might become a user of their service. Or you might get a user to pass the code onto you. And that may have the effect of you getting the changes they made.
But they are not "giving back", and they have no duty to do so.
I know it's a subtle difference, but I think it's helpful to be specific when it comes to legality- it avoids misunderstandings.
