So, you copy someone's music, change it a bit, publish your version without even buying the original in the first place, and you're surprised that that's an infringement? Copy a book, change the plot a little, publish it under your own name and see what happens... If someone composes a piece of music they have a right to 1. be credited and 2. control who copies it, whether for profit or not.
You can of course perform someone else's music and publish your performance with the appropriate permissions and accreditations.
Remember also that the copyright holder may also feel aggrieved for artistic reasons if they don't like what you've done with their material.
To me that's simple natural justice.
Having said all that, many people put their own versions of songs on Youtube and other places without intending or causing any harm, but the rights of artists were hard won and need to be protected, and we should always bear this in mind.