It is theft of service. Same as if you went in for a haircut, and didn't pay for it. You just stole the service provider's time. The only difference with copyrighted works is that the multi-million dollar price tag on it is divided up among all the people who purchase it.
The harm caused is that you are denying the copyright owner their legal monopoly rights on distributing copies, therefore devaluing their virtual asset.
Ok, so let's break this down a bit further, and have a world without copyrights.
Say that I have an idea for a copyrightable work. It is going to take me one year to create it, working 8 hours a day. To make it simple, put a price of my time at $100,000 for that one year.
Now I could find someone to give me $100,000 as a fee for creating that work (assume that I have no other desire to make it for myself, so I would only do that if someone pays me). But now the problem is, to almost any potential customer, that work is only worth $10.00. So it doesn't get created.
Or, I could find 10,000 people to each give me $10.00 in advance to make it. Now this is in the realm of possibility. Kind of like the Kickstarter model. But now everyone either has to pay in advance, then wait a year to receive it. Or sign a legally binding contract that they owe $10.00 each once the product is delivered. This all adds friction to the system.
Can we invent some technique to remove this friction? How about, I'm willing to take a chance on the popularity of my work, and build it in advance. I really don't know how many people are interested -- it might be 10,000; maybe 5,000 or possibly 50,000. So with copyright, I can safely take that chance -- over time, if I create enough works, some may lose (not be popular enough), some may win big (and I make much more than the time I put into it). As long as it averages out, society in general is better off (assuming you think it is worthwhile for the works to exist to begin with -- I'm guessing this is true, otherwise you wouldn't be interested in obtaining it to begin with).
Now, does anyone have any other models (I mentioned the Kickstarter model already) that can equally reduce the above-mentioned friction? That is, allowing a creator to take a chance on making something in advance, and then on average extracting the fair fee for everyone who wants that service?
IP law needs to be reformed. It's deeply immoral in both general idea and implementation. Royalties should not be a thing, period. We are not in medieval England anymore, we as a society have ways of providing patronage that does not involve state violence. Apart from that there are live performances (which feed like 99% of artists).
And I don't really care about mega-production Hollywood. It can burn today if I care.
People doing business on someones content - no, that's not OK.
Copying someones work for your own consumption? Nothing is wrong with such behavior. Nor with non-commercial sharing. Not until you have disposable income. Then consuming and not chipping in is meh.
Legal positivism is has it's stronger sides, but this is victimless crime.
I think it's really important to be upfront with saying what you believe is wrong. It makes it really easy for people to dismiss an argument when all they read is "no, it is not stealing", particularly in this domain. It's too easy to roll this in with those who don't want to pay for anything, that all content should be free. You're arguing something different, which isn't clear until someone else digs down. I think you do yourself a disservice in doing so.
I don't think whether or not you have disposable income is an important discriminant. Who decides whether you have enough disposable income to justify paying for content?
I think there are a lot of issues with laws regarding intellectual property and content. Even though I disagree with them, I don't think flouting those laws is right or some sort of civil disobedience.
Same with copying someone's work for personal use or non-commercial sharing. The existing framework is the one we've got, and there are currently ways authors or content providers can make it clear that they are willing to do so: Creative Commons licenses are one example. Likewise with other patronage models, such as Patreon. In other cases, you're benefitting from their work without them receiving compensation. There's no agreed upon transaction. Whatever term is used to describe it, I don't think it's right.
I'm not the parent you were referring to either, but my view is that 1) yes, shamelessly 'pirating' is at the very least a moral gray area, and in my opinion on darker side of this area, and 2) calling it stealing is a gross oversimplification.
Concerning 2): many people I know who pirate, say, a particular show, would simply not watch if piracy was not available. On the other hand, once this show becomes easily available and accessible on something like Netflix, these same people happily pay for the content. It seems inaccurate and dishonest to call them 'thieves' by the conventional definition.
tl;dr: I wouldn't defend piracy in most cases (you could just not watch the show), but I think calling someone doing this a 'thief' is a morally worse because of what that words means to most of us.
This is a poor analogy anyways because time is money for most intents and purposes. Making a copy of a file doesn't cost anyone time or money as the work in question has already been created and the time has already been spent.
The harm caused is that you are denying the copyright owner their legal monopoly rights on distributing copies, therefore devaluing their virtual asset.