If I can be so bold, here's what I have to offer on why threads like this are reacted to in this manner, and why I, personally, count this as a good thing:
You are not devoid of value just because you've spent years doing something thankless. Musicians write because they like to, and sometimes after years of practice they get good enough to finish something in a matter of minutes.
Like a painter who might sketch a friend or family member, or maybe even complete a large work and give as a gift, musicians are by and large not selfish. In fact, they are so giving that people expect these gifts which require years of experience. The thing is, they often think "credit" is enough of a return. It is not.
I get that people out there are doing things on a zero budget and for fun. Trust me, I know so hard.
But I'm going to go out on a limb and say when you are expecting things without paying anything, you should find creative ways to show the artists you are not a thief. Offer a little something to the musician in return. If you plan on selling your creation but have no cash upfront, be clear and concise about how and when you will give them their percentage of profits. When people are offering the project for free download, I've had them offer to send drawings, I've had people offer to make music videos, or get me in contact with friends of theirs that run radio shows, or send me the serials to programs they are no longer using. Just generally they were being good people making an effort to show that they were not taking me for granted.
Just somehow show that you respect these people helping you out, creating something special for you. That you think more of them than as a way to get quality assets for free. It's real time and often it's real money that goes into the free, short things.