No it isn't. It's called copyright infringement.

> Yeah, that's called theft.

Only by loose metaphor; its actually properly called "copyright infringement", which is more analogous to trespass to chattels than to theft, or even conversion (though it obviously differs from either in that copyrights are intangible personal property, and the others deal with tangible personal property.)

That's certainly the legal doctrine. Personally, I don't happen to agree with it.

How? I honestly don't understand how a person in the same ethical framework could disagree with this, if he fully understands the situation.

Here's one way: once you release something publicly enough it becomes part of our culture. You don't own our culture, any part of it, even if you created some of the art in it. Your work lives in a context surrounded by other works you did not create, and could only have been created as a response to them. That's how art works. So while you have some rights to it, you don't have absolute and complete rights to determine what happens to it after release; it belongs primarily to society now, with a respectful nod towards you. People are free to talk about it, watch it, look at it, listen to it, learn from it in ways you never imagined. And you won't get paid for all of them. Welcome to creating art.

Ethic and morality judgement is very subjective endeavour with inconsistent results across the population. In other words, most people do not exist in "the same ethical framework". The justice framework used by judges is perhaps more consistent, but not necessarily better than other competitive view for any case in hand. Sometimes the very laws are very immoral.