For Science!9 Things That Would Actually Happen to a Superhero Exposed to Radiation or MutagenFor Science! - RSS 2.0
2. Gain the power of... Reduced life expectancy!
Each of the beneficial mutations we covered is caused by a small change in the DNA sequence. While you can argue that a larger change would create a larger beneficial mutation on the scale of a superpower, it just doesn't work that way. Your DNA is like computer binary code; randomly change one of the 0s to a 1, and it's possible that result will be an improvement to the code. But the more random changes you make, the more you're likely to end up with a Blue Screen of Death.
A number of genetic diseases are attributed to mutations: sickle-cell amaemia, cystic fibrosis, and Huntington's disease are just three examples of disorders that shorten a person's life expectancy and quality of life. They are caused by "faulty code" in the DNA, 1s and 0s that are out of sequence, causing errors in the program. Our DNA evolved into a complex sequence suited to maximize our survivability; random changes are more likely to do harm than good.