How does it hurt those who create music? Your post has me intrigued as I fail to see how it cost the creator anything to upload the content to the site hosting the streaming, or how it cost them anything for the content to be hosted on that site's servers.
OK, lets try it this way for clarity. Perhaps not brevity, but hopefully, a tad more clear.
I think there is some confusion, so I'll wind my way through a few possible answers. Not sure what your question is, so forgive me. Corrections are welcome, as always.
If you are a writer or musician, your goal is to sell books and music. Everyone that downloads unauthorized copies of your book or MP3 file is not paying for the music and there is no difference between you illegally downloading and slipping the CD into your pocket while at Best Buy.
Bottom line is the creator looses money, either way.
So as you enter Best Buy, I tell you that if you go to this address, you can get copies of music for free. Just provide the media and they will make you a copy. Did I break the law? I do not do the copying, just providing the address where you can go. My goal is to provide you with free music and I have not broken the law, specifically, but perhaps I have.
The creator is free to do as he or she feels and if artists want to upload their music, they have this right. We are talking about illegal materials and illegal downloads. Quite a difference between the decisions the creator makes and the decisions others make to my/your stuff available to the world.
I create music. People seem to like my crap, so I decide I will become the next Earl Scruggs by spending loads of time in the studio recording my epic and decades perfecting my craft. My CD is done, The Grand Old Opry is in my future, and the tour bus is being customized.
That CD or those MP3 files are mine. I own them and only I, me, Bob, have any rights to my stuff. I can give the music away, post it on YouTube, or my web site. I can charge $4500.00 for a copy, or fifteen cents per track. I can sell one of the dozen songs, all 12, or make a sampler.
You, on the other hand, have no rights. None, Zero, no rights to copy the files and post them anywhere. I however, can grant you rights, but that is my decision, never, ever is it your decision.
So, you decide that you want to post a link to my music. You know you do not have the right to copy my crap so you decide the safe thing to do is just post a link. And your goal is to help others violate my rights. One could consider your act as the facilitation of a crime. Actually, no bones about it, you are making it easy for thief's to steal my songs.
On the other hand, what you are doing is perhaps legal as you did not break any laws, yet. The law is both clear and not so clear. Some people post complete articles and music claiming Fair Use. Or they post video to YouTube claiming that they do not own the music, but they lay claim to copyright protection in their name for the post (if they add lyrics, for example). Many also tell the viewers that so and so owns the music, not the poster, as if that makes any difference.
Simply put, YouTube is a place where IP violations occur hourly. We have lots of people breaking the law and claiming protection they do not have or deserve.
So the question becomes this: if you make it easy for others to break the law, what consequences should there be for you? If my web page contains links to thousands of illegal downloads, should I/You be accountable for perpetrating an obvious crime?
There is the problem and as I have said, it will take a court to rule.