Why stealing is different?

Because you can't usually take something by accident. If you did, and you could reasonably demonstrate that it wasn't intentional (rather than just saying "oh I didn't know it was in my pocket"), then you might not be convicted of theft.

As for “trying” to label copyright infringement as a crime, I did not do that, I just stated that it is unlawful.

You're right, you didn't say that. I apologise, I lost track of who I was replying to in this long thread (I wish Lemmy would give you a ?context=3000 thing like reddit did).

Copyright infringement is indeed illegal, in any form. It is a civil offense at the base level, meaning the rightsholder has to prosecute it themselves, however it can escalate to a criminal offense if certain conditions are met. This never used to be the case, back when all the Napster trials happened it was only ever a civil offense, however over the last decade or so media companies have been successful in lobbying the government and changing the law. I just hope they don't manage to change it further - rights like the right to record live TV on video were hard won and shouldn't be undermined.