This answer assume that the blind people are, as stated on the question, on a stone-age development state, and doesn't currently have access to modern times technology. If they do have access, please leave a note and I will change this answer accordingly.
Having eyes is one of the major adaptative features on earth animals. They enable you to work on environment while on a safe distance of anything dangerous. They enable you to find fruits, to hunt, to evade things that are hunting you, to read and write, to... well, a ton of stuff. If everybody would go blind, we would have so, so many problems that I doubt human race could survive five or six generations. Let's get into detail.
Problem Number One: Food
Imagine that you must grow wheat to survive. And you are blind. You must prepare the soil, distribute the seeds, check if the plants are ok from time to time, apply fertilizer if needed, and them, when they mature, harvest them.
Preparing the soil would already be a big problem. Without sight, you can't really tell were you are without some sort of reference point at hand-reach. And... in the middle of a huge wheat field, what you definitely doesn't have is a reference point at hand-reach. Even if you put landmarks from time to time with ropes scattered everywhere, how would you prevent yourself from getting lost? A big, huge farm is not the same thing as a complex urban environment with tons of different reference points scattered everywhere. Even middle and small sized farms would be an issue.
Tending the crops would be even worse. Without eyes, you wouldn't be able to tell the difference between weeds and wheat until is too late. Without eyes, you won't be able to check if the crops are okay or if they are sick. You can't tell if there are flocks of crows eating your crops. You wont be able to tell the difference between a good, edible fruit and a poisonous one if they are pretty similar.
Gathering food would be almost suicidal. If you go to the woods to pick up some berries, there would be tons of animals ready to bite, claw or sting you with no mercy. Go too close to a snake, miss that deadly scorpion over there, or run into a pack of wolves. Without eyes, you can't fight back. You would be food in a blink. Also, you can't run: Being blind and trying to orient yourself in the woods or any type of difficult terrain is almost impossible at a fast rate — you need to be constantly checking for obstacles to avoid tripping, and if you trip while running away from a bear — bye bye.
Problem Number Two: Communication with other people
Letters are easy. You can write some stuff on paper and then it stays there, ready for you to read it later. Text is a fast, simple, and efficient way of storing information. Remove the eyes of everyone, and almost all the knowledge would be irreversibly lost. People would lose all sense of geography without maps, and even reaching another city would be a huge problem. Without the stars or the moon to tell you where you are and where are you going, overland travel and sea navigation would be impossible. Settlements would rarely enter in contact with each other, and would in turn become more and more isolated from each other, cultures diverging more and more, until you have two completely different peoples with even different languages.
Problem Number Three: Medicine is Impossible
Good eyesight is a must today, when we have the extremely advanced machinery to help us to treat people. If you have a blind doctor, by the time he finds the cut that you made on your leg while running away from the wolves you would already be dead.
Problem Number Four: Child Rearing
I will keep this one short. How do you find your toddler? If you took a nap and that little brat escaped from his bed, how would you find him? He can be under the bed. He can be outside, in the garden. He can be on the belly of that mother-wolf that is tending a new litter of puppies — blinding all the humans would be a nice thing for them, that's for sure.
Problem Number Five: Social Life
With eyes, we can see who is around us. Without them, you only would be able to tell if someone is there by their voice. Where are your loved ones? Where are your kids? Are they sleeping? Are they gone? Is there someone strange on your house? You can't tell if they don't produce some sort of noise. While you talk to someone else, who is listening? Are you sure that you are alone?
Keep in mind that having eyes is one of the most basic evolutionary traits of modern animals. Those that don't have some sort of vision normally inhabit pitch dark caves that wouldn't be a good place for humans. Losing eyes is a major setback that can destroy an entire population really quickly — even humans.