Copyright is a state-mandated monopoly on reproducing a specific creative work.

I agree.

Violating the state's rules about that monopoly is not "theft".

Wrong, because you are operating from a non-capitalistic mindset. The artist is not suddenly able to reap the benefits of socialism or communism simply because you wish the economic system to be different. We can distinguish between public, private, and personal property all we want, but they're nonetheless still unrealized concepts. The artist must still eat, and depriving them of their work by feeding it into a plagiarism machine is not a step towards tearing the old system down; it is in direct support of it.

So you can handwave and be a legalese pedant all you want, but the reality is that copying art in this current economic system directly deprives the artist of their livelihood. Sounds like theft to me.

ETA: if you don't care about artists, then just say that. At least it would be honest.