The difference between theft and copyright infringement is one of immense philosophical complexity.
Deprivation of property is nothing more than deprivation of the labor entailed to obtain that property. You bought a car? That cost you $28,000, which you worked for; but why did you work for $28,000? Because the car salesmen spend time seeking out, talking with, and servicing customers; the cashiers spend time being available to take your money; there are delivery drivers who must bring SIX CARS from far-off to stock them in this enormous 500-car lot; someone makes those cars in the factories; someone makes the steel, the paint, and the plastics; someone mines for the ore, and produces the power required to make those things. These are all human labors, time which must be taken to make the thing.
If someone steals your car, they steal the outcome of nearly $28,000 of labor. It's probably more like $24,000-$26,000, and only that high because the automaker has negotiated for bulk purchase of steel and paint at razor-thin margins ($1 billion of profits at 0.1% vs no profits at your usual 15%, Mr. Carnergie), and the steelmaker has used the promise of an enormous contract to bid down the ore and coal miners on contingency of receiving and maintaining the automaker contract. These people's labors also went into production (organization and operation of production, which means less total human labor than self-organized artisans). You have to fork over all that cash to get a new one, or else insurance has to fork it over (and insurance rates are slightly higher than costs, meaning the cost of basic levels of theft is paid by the insured).
Theft isn't about tangible, physical objects; it's about time.
On the other hand, if you make copies of a work, that deprives no one of tangible property. There is no cost of labor of pressing a DVD for which you have stolen a man's life and livelihood; there is no cost of labor of shipping which you have taken without payment; there is no plastic or metal or ink which a man has made with his time and for which you have failed to pay. Why, then, would it be theft?
Movies are made by the labor of screen writers, actors, special effects artists, directors, producers, marketers, musicians, sound engineers, construction workers, fuel miners, energy producers, iron and steel manufacturers, and so forth. Seemingly-endless human labor time is poured into the production of a small piece of information, a tiny thing which you can reproduce with hardly a fraction of a penny's worth of additional human labor.
It is for this effort they demand compensation.
What justification do you have for depriving these people of compensation for their labor?
The only justification is that your particular action doesn't cost them anything, directly. They only labored at what we price at millions of dollars of wages to produce a thing which can then be copied for a fraction of nothing; you only took that fraction of nothing. They expect, for their work, some form of compensation, and you don't see why you should give them such a thing.
That is the philosophical comparison of theft of property versus theft of intellectual property. That is why it's called "intellectual property": it really takes the labor of a man to make it.