Expanding bullets vs solids. I'd like to point out what I believe to be the main point between the two and their purpose in my mind. It's much like shotgun chokes.

The reason we don't us solids on lighter, thin skined game, 2 or 4 legged is because the solid will pass on through, not dumping it's energy in a vital area. So, we use an expanding bullet to help dump that energy where it will do the most good (or bad depending on your point of view).

On a heavy, thick skinned, boned and muscled critter you need to penetrate to the vitals and dump that bullet energy there to do as much damage as possible there. An expanding bullet will just not get to the important stuff.

Just like there is no good or bad to tight choked vs open choked in a shotgun in general, there is no good or bad in expanding bullets vs solids. The main idea is to get to the vitals and do the damage there, not before and not after.