Yes, but aren't most mutation's negative? Look at the number of genetic diseases in humans. Now look at the number of postive mutations in humans that we have identified.
It seems to me that the overwhelming majority of mutations are negative. Many of those will be culled from the gene pool before they can reproduce. But not all of them. Many of the negative mutations will reproduce. Repeat...repeat again....repeat again.
Negative mutations are spreading through the gene pool. Without significant environmental pressure, it seems like the natural course for any species would be to decline over time.
Thus I'm formulating a new principle, that says any species that becomes dominant shall begin to degrade in the absence of sufficient survival pressure. Let's see I need a name for this principle. "The Peter Principle" - no been used already for something similar. "The Principle of Natural Degradation of Dominant Lifeforms" - too long. "De-Evolution" - No, coined before me and is bigger in scope than this principle.
"Dominance Paradox" - Hey I kind of like that. Any lifeform that becomes dominant enough that minor negative mutations are not immediately culled out of the gene pool will begin to degrade. Discovered here today by DannyTN.
Let the Pee-er mocking of new ideas begin!
Some are. Some aren't. Here's a thread from two days ago Ice Age Ancestry May Keep Body Warmer and Healthier which discusses favorable mutations. I don't know why you imagine mutations must be unfavorable. A mutation might make you smaller, or maybe taller; weaker or maybe stronger; allergic, or maybe resistant to an irritant, etc.
Besides, death takes care of the truly unfavorable mutations, and the rest -- however few they may be -- go on to breed the next generation. Evolution keeps increasing its bets on the individuals that survive. Every species now living is a consequence, and those species are but a tiny fraction of all the species that once lived. Each of us is a long shot, but here we are. That's evolution.