Even if we can push Earth around to keep it from getting fried or frozen,
or keep Sol still fusing past its due date, how long will the natural
resources on our planet last to maintain a developing technological
civilization and an ever growing human population? And even the other
bodies in our Sol system, which I assume we will utilize and colonize.

Assuming humans do not radically change any time soon, we need to
spread ourselves out in space in order to ensure that some of us keep
the species going. And again I propose that we genetically engineer
people to survive in all sorts of cosmic environments.

Maybe we will get through with our society relatively the same as when
we were young, but our children's children may not be so lucky. I am
not even talking about some terrible disaster here, just the fact that if
we stay put on Earth and keep living and growing the way we are now,
resources will run out one day.