> I can understand the MIT license, and my corp lawyer can easily understand all the consequences of using something under MIT license.
Sounds like you need a better lawyer.
The consequences of the GPL are not all that complicated. In most cases it boils down to offering the source if you distribute the code outside your organisation.
Therein lies the problem. When dealing with the law, you don't want to be relatively sure that you won't go to prison or won't get sued for $1M, you want to be completely sure.
Something like the GPL is complex and non-standard as far as its interactions with the legal system go, because it is essentially a sort of hack of copyright law. If it goes before a court, you have no idea what might potentially happen. So rather than deal with that kind of complexity and uncertainty, you'd use something under MIT or Apache License that is just much better understood.
> Therein lies the problem. When dealing with the law, you don't want to be relatively sure that you won't go to prison or won't get sued for $1M, you want to be completely sure.
Not really. Unless you are redistributing it does not affect you at all.
> Something like the GPL is complex and non-standard as far as its interactions with the legal system go
it is widely used, and most people are running some copyleft software anyway, most commonly GPL or a variant such as LGPL. Linux servers, Android phones, routers, web browsers....
Say you have linked against a GPL'd dependency which you have not modified but for which there is no API-compatible substitute. Are you now bound by the terms of the GPL? FSF says "yes", which tends to surprise people. But if there is an API-compatible, non-GPL'd substitute, the answer arguably becomes "no". Note that this has nothing to do either with your work or with your direct dependency, but on the existence of some random artifact out in the ecosystem which may come into existence at any point in the timeline.
API is not a random artifact but a dedicated feature designed to separate one program from another. It also implies much more stability for the external connections to the code.
It's like saying that display is a "random artifact" of a computer not making any difference in its design or usage.
Sounds like you need a better lawyer.
The consequences of the GPL are not all that complicated. In most cases it boils down to offering the source if you distribute the code outside your organisation.