I agree. Our (human) DNA is inexorably bound to this planet. We have evolved to fit this place before it was fouled, and here we'll stay. Except for visits, of course.

What we need for life is so complex any colony will have to have a huge input of material from Earth. And it will never be robust enough to tolerate an epidemic of some mutated illness.

For instance, what would happen on a small colony if it developed Hepatitis X? How would it research the illness, find an appropriate palliative or cure and manufacture it?

Nanotechnology might be available to automate that process, but by then we wouldn't, as you suggest, be human. Homo, maybe, but not sapien.

I think the Universe will be as kind to our species as we have been with others. Nothing sacred about Homo.

Arf