Terraforming

For those unfamiliar, the act of Terraforming is defined as:

To transform (a landscape) on another planet into one having the characteristics of landscapes on Earth.

(Further reading can be done at http://en.wikipedia.org/wiki/Terraforming)

The question I have is this: Do you feel that attempting to (or perhaps successfully) changing another planet's ecology into a form that would be capable of sustaining human life would be ethical or immoral?

I figure this might get some activity.