So someone washes your car, and you drive away without paying them. You have taken their time and labour away from them, exactly what happens when you pirate software, moveis etc.
The dudes on the highway make this exact insane argument. Here's the deal - if you really want to make sure I pay you for your effort, get me to agree with it beforehand! Hell, the whole kickstarter thing is essentially built on that idea, on making people pony up the money up front. If you do a bunch of work, and then I benefit without compensating you, it might be a dick move but it is NOT stealing.
Stealing, in this case, would be if I approached you with the offer, agreed to pay you, and then skipped out - in that case, I would clearly have been stealing your time, and even if I had no benefit whatsoever (drove through a mud puddle on my way out the driveway?) you would still be the worse for it.
But here's the problem - a lot of people are, a lot of creators and developers, are entitled fucking brats who think just because they put in the effort the world owes them something. It doesn't! And thank god the world doesn't work that way. No matter how much work you put into a piece of crap, no one is under any obligation to give you money for it unless they actually agreed to it first. Even if they end up benefiting from it!
I think the better point of view here is to round up all the entitled asshats who think simple effort is enough for them to be rewarded and give them a nice big reminder that that isn't the way the world works. No matter how many times that asshole on the highway squeegies my window, I'm not giving him a dime. And that is not, it really is not, stealing.
Especially since, in this situation, the people pirates are supposedly stealing from (the publishers) aren't even the people who went through the work of squeeging my window! No, you're asking me to pay the guy who pointed him at my car, and hope the squeegieman is compensated appropriately.
It's a joke to call something like that theft.