It's actually quite popular among environmentalists. We need to make progress on sustainability, and we will. We CAN sustain 8 billion people because of the immense progress humans have made in food production and efficiency. Pretending the only solution is, less humans, is antithetical to everything humanity has accomplished.

Sorry for the pedantry, but Earth is not a "relatively small" planet. It's actually quite large for a rocky planet. Out of all the rocky planets and moons in our own system, Earth is by far the largest (except for Venus, which is about 90% the size). From what we're seeing with exoplanet research, it looks like Earth is still pretty large, though it's hard to tell since we have a hard time detecting smaller planets, and the "super-Earths" are more easily visible to us.

Of courses, compared to gas giants, Earth is small, but that's like comparing apples and whales.

"we" is doing a lot of heavy lifting in your sentence but we're about 2 centuries away from complete population collapse of the species.

There are less babies born on this day than any day in history, and that will be true for the rest of our entire species' existence, barring major technological "Brave New World" style test tube baby advances (which are indeed extremely likely given this fact.)