"If you just reproduced asexually your entire population would be very similar and therefore at risk for being completely wiped out by disease, environment change, or a better species. "
Theoretically. However, that doesn't explain how the simplest life forms continue to exist since they reproduce asexually. Not only to they exist, they develop mutations so the population continues to exist. I think you're short-changing asexual reproduction.
All true, but asexual reproduction isn't quite as fun...