The point that I was trying to make was this: Earthly resources are finite - but contemporary political/economic systems treat them as though they are infinite. This means that the shit-is-going-to-hit-the-fan in the next two or three generations. We already seem to be nearing 'peak oil' (i.e. the point at which becomes too expensive to exploit remaining reserves of fossil fuels). In addition the climate is changing as a result of global warming. This is already having a deleterious effect on farmlands, and hence, in the near future, will badly affect our ability to feed our ever growing populations. We can only expect such dire effects to get worse.

The degradation of the environment, here on Earth, can only lead to misery, conflict and the destruction of whole populations. I doubt whether anyone will have either the will or the ability to embark on such a stupendously difficult and expensive undertaking as interstellar travel!