If you choose not to pay for their movie and watch something else, you are correct that you didn't steal from them. You did steal from someone else just like them though. If you pirate their movie, then yes you did in fact steal income from them. The act of choosing to pirate that particular movie changes it from a matter of potential income to a loss of actual income.
Right, so that isn't stealing. It is in fact what I advocate strongly. If more people did that, more content they would enjoy would be provided at a reasonable cost.
But extracting the value of watching something without paying the fee for that service...that's stealing.
If I can't buy something for a price that's worth it to me, I will just watch something else. It doesn't mean I'm going to pay more for it.
You get the same amount of money either way.