a lack of diversity is only really bad in a changing world. however humans have made the world far more stable than before, and as we move our civilization into space, we'll find likely more stability (in the long run)
You must be kidding. Humans have changed their environment almost beyond recognition. We may already have broken ourselves, look at birth rates in the most industrialized countries.
That is pretty optimistic
This is how we play for time, this is the whimpering with which we fade out. Looking straight at the iceberg, saying "it'll probably transform to cotton candy if we hit it fast enough". The drunk captain and the armed guards letting no sane person near the bridge is how you know everything is fine.