Much of this has to do with making it harder to steal music at the request or demand of music labels or those who own the distribution rights. Apple is the largest distributor of music in the US if not the world so many more watchful eyes are upon them.
There is a warning message provided, which you were provided or you wouldn't be here.
iTunes includes an option to transfer iTunes content that was purchased/downloaded from the iTunes store from an iPod, iPad, and iPhone, but this is for iTunes content that was purchased/downloaded from the iTunes store only.
With your computer authorized with your iTunes account with iTunes, with your iPad connected and without syncing at the iTunes menu bar go to File and select Transfer Purchases From - the name of your iPad.
For any iTunes content not purchased/downloaded from the iTunes store, there are a number of paid utilities that provide for this which are not supported by Apple.