You have confused ideas with property.
And you are confused to think all intellectual property is ideas, whereas the reality is things like songs are based upon ideas, but are not ideas themselves. Songs are air vibrations created by instruments or human voices and ideas are ueed to guide these vibrations -- so songs are not ideas. Songs are tangible (to the ear) whereas ideas are abstract.
Just as a house can be based upon ideas (such as ideas about location, ideas about exterior design, ideas about interior design etc), the house is not ideas, rather it uses ideas just as songs use ideas.
The only rational argument for using state force to punish people or make them pay for making a copy of a work is that doing so promotes the creation of more works.
When you derive benefit from a commercial product, such as a song, without payment, that is theft, pure and simple. Your argument that the owner is not deprived of his copy is irrelevant. The music was created to be listened to by consumers in exchange for payment.
if I sing one of his songs it doesn't -- and so your comparison makes no sense.
I'm sure if enough people hear it, it does make a difference. You're using somebody else's hard work for your own gain (whether monetary or not) and it dilutes the value of that work even if you give it away for free. This results in lower sales of said song.