mars and venus are the first step. we aren't going to jump out of the solar system on our first try. we will be lucky if we don't have a lot of failures in that endeavor, even after the experience and materials we gain from the solar system.
>Moreover if death is natural process
humans are also a natural process.
>some alternative star may born by that time.
you mean a new star is going to come to our solar system before the sun dies? I think I must be misunderstanding. If not, that's asinine.
I don't really get how you can call it fearmongering. who is supposed to be afraid? most people only think as far ahead as two generations. the only people who are disturbed by your strange brand of environmentalism are people who think hundreds of years into the future, ie other environmentalists.
http://en.wikipedia.org/wiki/Timeline_of_the_far_future
your billions figure is also a gross overestimate. our timeline is not so generous.
and don't forget that life took (actually) billions of years to evolve. what are you trying to protect on mars and venus that is more important than that?