I don't mean it is not important, but it doesn't change how society thinks about things in a significant way. Evolution theory offers an alternative to the explanation that "god created everything". That affected everybody, not just the scientists.
If endosymbiosis were popularly understood, society might better understand and acknowledge the connectedness of life on Earth. Instead of humans treating the planet as their own kingdom and garbage dump, they might develop a more harmonious, respectful relationship with the natural world. That might lead to greater prospects for sustainability of the planet and of humans.