well if the chicken needs the rooster to fertilize the egg and only by fertilization can there be any dam in the egg, why do we bother to check the eggs for spots?

Why do you assume that blood spots are only the result of a fertilized egg?

well if they are not there from fertilization then they are not considered "dam" and the egg can be technically eaten as per an Iggros Moshe I once saw

But you as the consumer will never know whether or not this egg in front of you is a fertilized egg or not.

an member forwarded this link to me

and now after learning this gemara we all know why the chicken crossed the road

Its a rooster,not a chicken. Its a bridge not a road.
That said it always boils down to one thing.