I would write The buy-nothing-day activists because the three words make up a whole unique notion.
I think some articles should be cleared off, I mean those which come with abstract terms. ...demonstrate against overconsumption. (...) Overconsumption is harmful to environment (not "for"). (...) it leads to depletion (...) I think that it is unfair (it, not he; just a slip of the pen) (...) Overconsumption leads to rivalty between people.
Si sa peut aider