There's nothing wrong with the McDonalds analogy; it's perfectly apt. The "kitchen" is the WoW engine and assets. You don't get to help yourself and put together a version you prefer.
It's shitty that there's no official way of playing Vanilla WoW, but you're not entitled to it. Also, there's no question that some of the people who play Nostalrius may otherwise be paying Blizzard to play WoW if they weren't instead playing this for free. You can argue all you want about how small that number of people is, but it doesn't matter. If Nostalrius costs WoW even one subscriber, then that's lost revenue. Lost revenue due to IP theft, I might add.
And who's to say Blizzard will never revive vanilla WoW in future? Nostalrius would kill any chance of that. And if it did happen at some point in the future, the existence of Nostalrius now would hurt it, as people will have already had their nostalgia kick, and will have no reason to subscribe. Somebody earlier in this thread praised Jagex for RuneScape Classic, but it was years before that was brought back. Do you think they willingly let people run their own private servers during that gap? Of course they didn't.
But apparently IP theft and revenue theft (be it current, or destroying the financial viability of future possibilities) are things a company should just overlook, otherwise they're the bad guys.
I don't begrudge anybody for playing Nostalrius at all. Hell, I may have considered it had I known of it. But there's a clear line between what you want and what you're entitled to. If I had been playing Nostalrius, then I'd have done so with the understanding that Blizzard could pull the plug at any time.