Penn State Extension does not recommend eating tomatoes with signs of blight. They are not unsafe to eat, but blight spots are optimal growing conditions for other microorganisms.
Blight is a fungal infection that will quickly spread throughout the garden. It can spread to neighbors' gardens and farms as well. If found, the affected plants and vegetables need to be disposed of by wrapping them in plastic and setting them in the sun so that the fungus is killed.
Tomatoes that show signs of blight should not be used for canning. Canning blighted tomatoes will raise the pH level of the tomato, making it a haven for other bacteria to grow.