This has a good script, about ideological cultism and doomerism, and to my eyes, white supremacy and genocide. I don't read it as having an anti-environmental message at all (even before the Doctor's little speech at the end), but rather a warning about how easy it is for people across political and ideological lines to fall into fascism. And despite Lis Sladen's sense that Sarah was too passive in it, I think it shows her as a really strong character, largely by keeping her separate from the Doctor. We also see some of her journalism background at work.

It is, however, too damn long. Four episodes, omitting some of Sarah's and the Doctor's repeated captures and escapes, would have been much more suitable.