[kcindric]

Earth and its systems are too complex and left with too much unknown variables to be confident in messing with them without the danger of creating a feedback loop that makes the matter worse.

Take for example invasive species of plants and animals -- some of them were deliberately spread to non-native habitats in hope to regulate X but are now wrecking havoc in local ecosystems and pushing out native species.

[nomel]

I don't understand this. If people cared (or perhaps comprehend) complex feedback loops, we wouldn't be in this mess. If the majority of the human population starts suffering, including you and I, we will certainly do whatever we can to stop prevent that suffering, short term. I don't think there's any evidence, from any point in history, that suggests we'll, as a collective species, shun our instincts of self preservation, and die for the unknown of possible future problems.

Let's say India (they seem especially vulnerable) starts having mass heat and starvation, where they're losing significant parts of their population, and decided to slow it, immediately, by launching some solar shields. Do we shoot it down?

I think "never" is ludicrous. Once people start dying, people will demand and plea for something to be done, or heads will roll.