"I think it's that if we can't avoid damage to multi-billion year evolved, robust ecosystems on our home planet, we might not successfully craft off-planet ecosystems that will sustain us indefinitely."

And so...?

Even if true, that doesn't lead anywhere. If you're trying to faintly imply we shouldn't try, you ought to bring the arguments up to the surface, where examination will quite likely show they don't have that much substance.