Space Colonization

There has been some discussion Here, and more disturbingly Here, and Here.
I wanted to make my case there, but there appears to be many people caught up in their own biases and misinformation.
Some of these people are Environmentalist Wackos to the level of self-parody.
I want to make some points:

1. The extinction of humanity is not an acceptable outcome.
2. Whether through our own actions, or by nature, the earth will sooner or later become uninhabitable for humans.
3. We do not know when, it could be tomorrow.
4. It will likewise at some point become uninhabitable for all life.
5. Barring some really amazing advances in launch technology, it will always be impractical to do a planetary evacuation, even if we knew everyone on earth would die.
6. This is not about saving the people on earth, or giving us a way to escape our own foolishness.The people who 'escape' will be called 'astronauts' and they will probably be numbered in the thousands, not the millions.
7. At that scale, talking about social representation is a bit silly.
8. Nothing about space colonization means we don't need to work to solve problems here.
9. The costs involved to bootstrap this process are negligible compared to global GDP, and what we currently spend on causing problems.
10. Much of what we learn in the process will be extremely helpful in solving problems on earth.
11. The earth's biosphere does not have any magical properties required for human life. There is no reason to believe that we cannot create a long term habitat, if we try.
12. Another threat to humanity is tyranny. One good way for people to free themselves of tyranny is to leave. If there is a large system of colonies in space, and we continue our expansion, then there will always be somewhere else to go.

I am afraid of ecological disasters, but I am more afraid that we will get stuck here with somebody in charge of us.