Here's the thing to remember with mutations: If a population is well adapted to its environment, then most changes will be changes for the worse. That is, most mutations will be deleterious.
I doubt that this is correct. Perhaps it could be true about organisms who are overly well adapted to some niche environment, but I would not expect that this is true for humans for example.
The fact is that most human mutations are somewhere close to neutral with respect to fitness. We know this because every human has mutations. It may be that most mutations that have some significant fitness impact are deleterious rather than beneficial, but given that such mutations are selected against, I would expect that even lop sided ratios of deleterious vs beneficial mutations would not stop the process of evolution.
Edited by NoNukes, : No reason given.
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