This is negative utilitarianism, right? For instance, if you could press a button and wipe out humanity without (much) suffering, would you do it? Personally I'd have a quick reminisce then all slam it.

But practically, this isn't an option (yet). Nor is voluntary extinction. The people susceptible to this message or any such message (better for environment; your group of people is bad and shouldn't continue; life is more fun without kids) are more likely to be the kind of people that would contribute to a positive next generation.

The bulk of growth that'll receive and cause suffering is from people that won't ever listen or heed such a message. Hence anti natalism will only increase suffering in the world.