If you make, have, or offer a product, why shouldn't you get paid for the fruits of your labor?
If you build a car and someone takes it without paying you for it, that's stealing. It doesn't matter whether you've built one car, two cars, or two million cars, if someone takes one without paying for it, that's stealing.
So, instead of building cars, you write a book or music or make records/movies... It doesn't matter whether you make a single "home" movie or produce millions of copies of a large production which you pay to have distributed around the world, if someone takes one without paying for it, that's stealing.
Same goes for software. Even Microsoft has special deals to help out teachers & students who might not have the money to go out and pay full price for their software.
Now... If you want to pirate a book, movie, software, or similar item because you are protesting something, just say that's your reason. But don't necessarily expect anyone to agree or support your position. (I add this because I often hear the "I just hate Microsoft, so if I can get a free copy of their stuff, I will" excuse, which is interesting because the person is also saying that it is the best product that is available and they just don't want to pay for it... Hmmmm... there are many freeware/shareware/linux versions of software available. If you don't like MS so bad, there are other choices. Anyway, I digress...)
Regardless, the question at hand is:
Why shouldn't someone get paid for the fruits of their labor?