Delete a playlist on iphone through itunes

So I wanted to add some music to an old playlist. I synced the new music to my iphone and added it to the playlist but there was no way to delete the old music from my playlist from itunes so I had to delete it from my iphone. When I did this and re-synced, all the deleted music came back and made a duplicate playlist with a 1 at the end of it. I ended up deleting the entire duplicate playlist and set up a new playlist with the new music and the old music that I wanted to keep. Why is there not a way to delete a playlist/music on your iphone from itunes so that it won't just reappear when you re-sync it?