Why itunes is deleting all the music in the ipad or ipods? they have not permission to do that!!!

That's it, i connected my ipad to itunes, i have just updated to ios 8.3, and i have itunes 12.1.1.4, and it deleted automatically and without my permission all my music in the device, i have always automatic sync off because that function is the worst thing, and even with that set in off it deleted everything, buying an ipad or ipod to this company doesn't gives them the right to manipulate or dispose with the content of the people!!!, i am very furious with this actions taken by apple, thats the way they make good for the people that buys their products???!! So, what does have apple to say about this??