It is tragic that certain individuals lives are effectively destroyed by losing a genetic lottery, but in the end genetic diversity allows a species as a whole to adapt and deal with unexpected changes in their environment. Even for mutations like FOP there's the possibility that it could benefit humans in the long run.

Perhaps a slightly altered form of expression would allow for faster bone regeneration or a reduced chance of osteoporosis. The most relevant example I can think of is Sickle Cell Anemia. Having homozygosity for the mutation causing SCA leads to a multitude of complications and higher risk of death, but heterozygous humans have a significant increase in resistance to Malaria. Mutations are a blessing to some members of a species and a curse to others, but without them life as we know it would never have existed.

It's actually impressive, that's a single mutation which causes bruises to heal as bone instead of muscle.