It annoys the minority of businesses who feel entitled to the free labor of strangers and don't want to give anything back. You see, some people are childish and the most visible mark of childishness is a sense of entitlement. This causes them to feel somehow cheated if you place a few conditions on code that is otherwise free, that no one is forcing them to use if the conditions don't suit them. I think phrases like "you mean I have to actually HIRE my OWN PROGRAMMERS if I really must insist that everything be done exactly the way I want?!" are often uttered with outrage during their corporate meetings.
I mean hey, launching a commercial product with most of the work already done for you, for free, is a nice racket if you can get it. But if the developers intend to allow this, they wouldn't use GPL, they would use a BSD-type license. For reasonable people, this is not a problem. Reasonable people think either "hey, this code is available for free and we have no problem complying with the license, so we can enjoy all the effort that has already been done for us and build on that", or they think "the terms of that license aren't compatible with our business model, or we're afraid of how a court may interpret them, so we can't use that code, oh well, this has not harmed us in any way so we really have no complaint".
For everyone else, there is a need to demonize whatever it is that doesn't perfectly suit them even though they are under no obligation to use it. Sort of like the Puritannical types who want to shut down "offensive" shows that no one is making them watch and criminalize victimless behaviors among consenting adults that no one is forcing them to participate in. The mentality is never this direct and honest, and always covers itself up with a phony excuse, but if not for that its motto would be "it's not good enough that *I* don't do something I don't like, oh no, I have to make certain no one else can do it either!"
You are not +5 insightful but more -1 moron. (or Linux/GPL zealot)
There are reasons not to use GPL not having to do with modifying code, but simply running the code. E.g. GPL'd libraries. I haven't followed what the issue is with GPL v3 as I simply avoid any GPL code due to the zealotry of most of those who advocate it.
In the late 1990s I thought about a 'what if' scenario: Say most people run Linux with a lot of GPL'ed libraries, then I am sure some provisions in the GPL would have to be altered as it would force people to do things in a certain way for which there is no reason. So suppose GPL'd libraries are required because they are used in the system and rewriting it all would be pointless, a waste of time, but especially means having to follow all changes and reimplement them too.
A commercial company is about selling a product for a given system, not reimplementing that system.
I am sure that legal action would take place and rule some parts of the GPL invalid, IN THAT CASE.
For me, I don't care much about interaction issues, because after the late 1990s I had enough of the inane whining about GPL misuse and zealotry of Linux users. I use FreeBSD and am free of all that rubbish, and of all the different versions of lInux with their idiosyncrasies.
FreeBSD has flaws, but I'm not going back to linux...
And about the GPL licence, what annoys me a lot is the lie in the preamble, which btw. should be removed from the licence itself as it is propaganda:
The licenses for most software are designed to take away your freedom to share and change it.
What was not present cannot be taken away. Most commercial software is designed to do something specific, and the license is for that. When you don't get source, you don't get the ability to modify that source and modifying binaries is a lot of work. So, you never really had the freedom to change it, therefore it cannot be taken away. I guess it was meant as 'most licences are not intended to give the freedom to alter the program', but then it should be written in that way. But no, it's written in this adversarial way, and from what I read by Moglun, at least the licence section. Well, he should have objected to this and if it was not changed, not allowed use of the licence text that he used by the FSF. But perhaps he's just happy to go along with this nonsense by the FSF...
I like the idea of the GPL, but not the propaganda in the licence, nor the attitude of the proponents...