Plastic bags were introduced in America in the late 1970s. They were considered great due to the fact that they weigh less then 5 grams but can carry up to 7 pounds and there extremely cheap.
Over the years more and more people have realized that plastic bags are bad.
Plastic bags are bad for animals because they think there food or the bags can get stuck on the animals and if the bag gets in the ocean oil and others chemicals collect on the plastic. Also turtles mistake them for jellyfish (their favorite food) and eat them.