I want to encourage 'corporate flexibility and social accountability'.
I do not want to encourage market-whale-individuals to attempt one-person pump-and-dumps on small(ish) global markets and further market opportunism & manipulation.
Personally I believe that the decision has little to do with environmental impact; I think that the btc opportunity is beginning to dwindle in various ways, so the focus shifts to other *coin markets where they can profit similarly using the same or similar tactics.
BTC specifically is made out to be the boogeyman so that the excuse doesn't disallow similar behavior with other coins in the future. I fully expect similar reasoning with DogeCoin when that opportunity dries up and they move to greener pastures for the third time -- inevitably when profit margins are greater elsewhere.