Extinction is not bad, nor is it good, it simply is. It is evolution.
No, it's not. Evolution is a process where species diverge. It can only occur when one species splits into two, and/or a species radically changes as an adaptation to the environment.
It isn't 'survival of the fittest' or any other moronic thing they taught you in third grade.
The fossil record shows that there were sabre-tooth marsupials in South America before the land bridge at Panama connected the two continents. There was no 'evolution' at play when the land bridge occurred and sabre-tooth cats moved into the range and out-competed the marsupials. There was only extinction. There were then fewer species living on the planet, for better or worse.