The reason aftermarket bars have a greater chance of breaking the stock mounts is that they are stiffer. The whole point of using poly bushings or a larger bar is to stiffen up the suspension. With that added stiffness comes added pressure on the mounting brackets, which are barely adequate for the stock bar. If you add a larger bar, you WILL eventually break the mounting brackets.
I broke one of my mounts with only the addition of poly bushings, stock sway bar. Once I had the mounts reinforced, then I added a BAT bar.
