It's not a matter of stealing. Theft is a poor metaphor.

Its a matter of preventing the economic systems that support sound engineers, voice actors, grips, actors, and makeup artists from earning enough of a living to produce art.

Consider what has happened to journalism since smaller papers lost the ability to support professionals.

The tricky bit is that GPL is built on top of copyright. In effect it use the legal precedence of copyright against itself.

They weren't arguing from a legal, but from an ethics point of view.

It's not "tricky", it's by design.

In both scenarios the person's property is being stolen.

Their property might be in the form of information, sure.

But one product being more widely distributed does not make any ethical difference. The fundamental is that the information/property has been stolen in both cases.

Copyright infringement has as much in common with stealing as it does with sharing. Both of them are ideological terms to paint the action in a certain light and neither give a complete picture.

There are a lot of things common to both scenarios, and a lot of things different. People understand that what makes the difference to you is whether someone has the legal right to use something, but it's just been explained to you that the spread of information is what is important to some other people (because you asked.) Your ethics don't define ethics and are not fundamental.

People break the GPL in order to steal from the public. People break copyright in order to steal for the public.

> In both scenarios the person's property is being stolen.

With material theft, the person that is stolen from looses access to what is stolen. This is true in the case of a GPL violation. But not in the case of classic copyright violation.

You might argue that copyright violation prevents extracting profit - but it doesn't mean the victim loses access to their property.

It's not a property in the first place. It's nowhere near like physical belongings and it shouldn't be treated as such.