I was confused for a minute, then I remembered that you don't actually have to accept the GPL as a user, only as an intentional distributor. So while the base version is GPL, the private version isn't - by default it's a hybrid of GPL and proprietary code.

Actually, you have to accept the license as a user to be able to use it. However, you don't give up your right to keep any change for yourself if you don't distribute it in a different format (e.g. binary). Whatever you do in your house is your business. That's probably what you meant (in spirit so to speak), though law wise it is very different.

>Activities other than copying, distribution and modification are not covered by this License; they are outside its scope.

Why do you say you have to accept it?

Because running software involves making copies of that software. This requires you to have permission from the copyright holder. The GPL provides you with that permission, without adding any further conditions if the copies are just for the purpose of running the software.

http://www.digital-law-online.info/lpdi1.0/treatise20.html

It is now well-accepted that copyright protects computer programs and other digital information, whether they are in readable source code form or are an executable program that is intended to be understood only by a computer. Copies are made whenever the program is transferred from floppy disk to hard disk or is read into the computer’s memory for execution, and those copies will infringe the copyright of the computer program if they are not permitted by the copyright owner or by copyright law.

1. Even if that's the current legal theory it's bullshit, and I can run code without having copies in ram if I need to.

2. 'if they are permitted by copyright law' Fair Use is part of copyright law, has that specific defense been challenged when it comes to software execution and caches in RAM?

Regarding 1, I really don't believe you can run code without copies, or copies of a derivitave work, being made in the process.

That said, I can't read a book without reflections in my eyes...

I could run it directly out of a ramdisk, or maybe transfer it to an embedded processor that can run it directly off the flash chip without even a processor cache. There's a whole variety of ridiculous things I could do to avoid the ridiculous restriction.

In practice I would trust fair use and try to use such as a defense if sued.

> I could run it directly out of a ramdisk

Hard to do when you were shipped a DVD.

Because that's the legal side of this. You can compile and run GPL software on your computer without agreeing to the licensing terms, but you may not do it. It is very unlikely that someone will check your HDs for offending uses, and besides, any use of GPLed software assumes an implicit acceptance of its license, so if such a check is happening, you would have to be there to say: "I have it but I am not agreeing to the terms". That sounds a bit silly doesn't it?

That's how the rules have been made, and not complying could be assimilated to piracy.