In North America, dandelions are invasive. That means they are not native here, and they crowd out plants that are native, disrupting the ecosystem. In Europe, where they are native, dandelions are fine.
If you want teachers to use a new method, you first have to teach them the new method. That is the step the New Math people skipped. If they had properly trained the teachers, the whole thing might have worked.
We use ours to bring more groceries home. If you take old bags to the store with you, you don’t have to come home with new ones.