I think they are more common than people think, it's just that most sites and mags photoshop them away.
So I asked our pal Dr. Pascal. He wrote:
Moles are in their vast majority completely benign. Otherwise, 99% of us would die from metastatic melanoma!
See the "Signs and Symptoms" and "Diagnosis" sections on this page.
One extra element that's seldom mentioned to the general public, along with a Doctor's intuition, is the importance of chronology.
The majority of cancers evolve on a SUB-ACUTE time scale, meaning over the course of a few weeks. Acute is within hours or days at most, while chronic is within the scope of months/years.
Usually, we notice something on our skin for the first time as if "out of the blue". But if a skin peculiarity evolves (grows and/or transforms) within, say, 3 to 5 weeks, it's time to have it removed and examined by a proper lab.
Hence the importance of monthly breast self-examination.
Note: not everything of sub-acute chronology is a cancer, of course!!!
Final note: the ABCDEFG are good reliable criteria for when to act (without panicking!), but they can never be infallible. Medicine is all about risk assessing and managing. We often remove something that turns out to be benign (>90%, easily), but on the odd occasion, something which showed no warning signs whatsoever may turn out to be nasty. Once out of 10,000 or 100,000 times.
Simply put, the money & time & human cost of treating everything that could possibly be bad, would be completely unrealistic. There simply wouldn't remain any time left for just, you know, living life.
I know such people, who spend almost their every waking moment "taking careful care of their health". That's a severe obsessive-compulsive disorder, and a guaranteed fun-killer of life's enjoyment...
The rule of thumb is logic, common sense, and perspective. Guns kill far less people than cars, and yet we don't declare panicked war on automobiles. I believe that any random thing less risky than crossing the street (after looking both ways twice) is something we should just take our chances with.