Mugwort - Friend or Foe?

Last night in my Green Medicine class I was told by the teacher that Mugwort is an invasive weed that while it does have medicinal properties, it is toxic to all other plants and stops them >from growing. Teacher thought I was nuts for buying Mugwort plants and putting them in my herb garden.
I bought them from you last year.
Do you agree with my teacher's comments? Is mugwort invasive and is mugwort toxic to other plants' >efforts at growing?
Due to her comments I am seriously considering digging up my mugwort and destroying it.
Are you selling toxic invasive weeds?????
Is your Mugwort actually somebody nice and helpful and not toxic???

Almost all plants wage a secret underground war with other plants, by secreting substances from their roots that inhibit other plants. How successful they are is seen by their success in crowded conditions. The most obvious victor in these underground battles is the black walnut who additionally happens to have toxic substances in its leaves and the falling leaves will kill many things under them. I don't think that mugwort is particularly successful in this battle, since I have had the plant in my garden and it is being crowded out by other plants unless I pull out the competition. I grow on sandy soil and maybe the story is different in clay soil. I also don't find it weedy. But again what soil one gardens on often makes a big difference. On my soil I find seedlings of greater celandine and motherwort very hard to control, but have talked to other gardeners in clay soil, where they are not very hard to control.
The other point is just because something is toxic to other plants does not make it toxic for us. In fact, I would stress that it is most definitely not toxic to humans or animals, and is in fact a valuable medicinal plant.
The last point is that anything can be toxic if you get too much of it. This is painfully true for medicinal plants. Foxglove is a life-saver, but in too big a dose it kills. Even salt can be toxic if used in too big a dose. Notice we do not sell poison ivy even though is is used to produce important medicines.