I'm honestly just really annoyed about this "society and environment"-spin on advise that would have an otherwise niche, but perfectly valid reason behind it (TFA: slow satellite network on the high seas).

This might sound harsh and I don't mean it personally, but making your website smaller and "being vocal about it" (whatever you mean by that) doesn't make an iota of difference. It also only works if your site is basically just text. If your website uses other resources (images, videos, 3D models, audio, etc.), the impact of first load is just noise anyway.

You can have a bigger impact by telling 100,000 people to drive an hour less each month and if just 1% of your hypothetical audience actually does that, you'd achieve orders of magnitude more in terms of environmental and societal impact.

And no, a million small sites won't "become a trend in society".

Plus, trying to signal your way to societal change can have unintended downsides. It makes you feel you are doing something when you are actually not making any real impact. It attracts the kind of people who care more about signaling the right signals than doing the right thing into your camp.