That is certainly a worthwhile concern.

Edit to be clear: I think it is a worthwhile concern, not a reason to condemn all ecoterrorist action. It is just important that such action be well planned.

I think it pales in risk comparison to stuff like regular war though, and that keeps happening. They blow shit up for maximum impact and effect. whereas I would hope ecoterrorists are at least motivated to attack stuff in a non-environmentally-destructive way. Or at least, pick targets that have greater positive global impact than local negative impacts, but that kinda thing can't be an easy decision.