This particular trained lawyer wishes that we could never talk about whether copyright infringement is stealing, ever again. It's 100% legally irrelevant.
There are laws against stealing physical property. Copyright infringement doesn't violate them. There are laws against copyright infringement. Copyright infringement does violate them. The question of whether "stealing" is good shorthand for "copyright infringement" is a total waste of time. The real point is whether the copyright infringement laws are good laws.
In fact, let's get technical about it. Here's what's going on under the hood. Both areas of law relate to the idea of "alienable rights" -- stuff that only you are entitled to do, that you can sell or give away so other people can do.[1] For example, I "own" my bike. That means I have a bunch of rights over it. I can exclude anyone else from riding it. I can destroy it. I can sell the right to destroy it. I can sell the right to ride it on alternate Thursdays. I can sell the right to sell the right to ride it. Or I can sell the whole bike so someone else gets the whole bundle of rights. Lawyers, with a flair for the dramatic, analogize this set of rights over the bike to a "bundle of sticks" that can be separated or kept together.
Example 2: I rent an apartment. My landlord "owns" the property, but she's sold me the temporary, exclusive right to decide who can come on it and who can't. I can let neighborhood kids run through the backyard or tell them to take off. But I can't charge other people to sleep here -- she hasn't sold me that right.
Example 3: I "own" this comment. I can sell or give away the right to display it at ycombinator.com (in fact, that's what I'll effectively do when I click "reply"). I can sell the right to print it worldwide in any medium. I can sell the right to make a movie adaptation. I can sell the right to distribute it without my name attached -- or with your name attached. Or I can sell the whole thing and let someone else dispose of all these rights ...
So when we talk stealing and infringement, we're talking about violations of someone else's alienable rights. When you take away all of my alienable rights over my bike, that's called stealing. When you take them temporarily, it's "wrongful appropriation." When you take my right to exclude people from my property, that's called trespass. When you take my right to decide who rents my bike, it's theft of services. When you take my right to decide where this comment gets published, it's copyright infringement.
So at this point the copyright debate becomes a little clearer, right? The question is which alienable rights should attach to instantiated ideas (intellectual property), and how long should each right last, and what should be the consequences for infringing each right, and can we give artists something that works as well for them as these exclusive alienable rights, and so on. When people say "copyright infringement is stealing," it's intuitive, emotional shorthand for "the same arguments that justify the rights attached to physical property also justify the rights attached to instantiated ideas." When people say "nuh uh," that's shorthand for "nuh uh."
So the answer to whether copyright infringement is stealing is that there's a bunch of reasons we attach various rights to physical property, and there's a bunch of reasons we attach various rights to IP, and some rights and reasons apply to both and some reasons apply to just one or the other. Which is to say, it's a pointless question. The analogy is kind of right and kind of wrong, in a totally unhelpful way. The useful question is whether the particular rights bundled into "copyright" are the best way to do the things we're trying to do.
Seriously, when I think about it, I can't believe how many hours have been spent on the internet debating this pointless question. The next time you're tempted to start, just link to this comment instead. Then take that time to make something. Anything you like. Even a LOLcat or a drawing in MSPaint. Put it in the public domain. It'll be better for the world.
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[1] You know how the Declaration of Independence says we're all endowed with "inalienable" rights? That's inalienable as in the opposite of the "alienable" rights I discussed above. That's why you can't sell yourself into slavery -- your right to liberty isn't alienable.
The More You Know.