Freedom is a complicated, annoying, thing, and sometimes having a freedom means you accept the consequences of that freedom. In the US, we have freedom of speech, which means we can bitch about our government if we want to. But that also means someone else, who has the polar opposite of your views, has the exact same right you do. And I will defend that person with my dying breath that they have that right, no matter how much I detest what they’re saying.
You have to keep that in perspective when you start talking about rights and legality. WooThemes had the legal right to do what they did. That doesn’t mean you don’t get to think that it was a dick move, and you may, but what it was, was 100% above-board. They were honest about it, and it was legal. The GPL affords us the freedom to make plugins, fork WordPress if we wanted, and do what we want, so long as we don’t restrict the freedoms even more.