Can I hang shelves on painted walls without using penetrating fasteners?
The bond will fail at the weakest point in the layers between your shelf and the actual structure of the wall.
Many people fail to account for the fact that paint really isn't intended to be subject to those kinds of forces and are surprised when it all peels off.  

I predict that you'll end up with shelves fallen to the floor with the paint peeled off the wall and still stuck to the back of the shelves.  

It's far easier to repair the holes from a few neat screws than it would be to repair the unknown level of damage which may occur when your shelves start pulling layers off the wall in unexpected ways.  

Having more than a handful of cats myself, I know how active the little fur-balls can be - and those shelves will end up seeing dynamic loads far in excess of the 4-6kg the beasties actually weigh.