You could peel all the gelcoat off a fiberglass boat and throw it away,
without sacrificing any structural integrity. Gelcoat is a porous,
cosmetic, alternative to paint.

When you find "baseball sized craters" on a boat, you're dealing with
an extreme situation that goes well beyond cosmetic gelcoat blisters. I
would agree that a boat with baseball sized craters should be avoided,
but that's not what one finds in most cases. I diagree that gelcoat
blisters are a "kiss of death" that should take any boat with typical
cosmetic blistering out of consideration.