When software doesn't belong to you because you haven't paid for it, that is 'the illegal taking of another person's property'. How is it not stealing?
Noun: stealing
1. The act of taking something from someone unlawfully
Verb: steal
1. Take without the owner's consent
"take" in this case, Being the Verb: Get into one's hands, take physically, "Take a cookie!"; "Can you take this bag, please"
Copying not being taking makes copying not stealing.
However, as i said, it is wrong and it's still illegal, it's just not stealing.