Edit: What on earth would cause you to downvote this?
Edit2: Thanks. I would still appreciate a comment if I'm 'doing it wrong.'
The author implies that we only have a rational interest in what happens during our lifespan. But many of us, through childbearing or other means, try to leave something of value behind us.
Irrational? Perhaps. But there's no reason pure hedonism should be any less irrational.
That said, we're not slaves to evolution and can make our own choices for our own reasons.
But when it comes to the vexed question of getting those genes to survive beyond our own mortal shell, the correct genetic strategy seems to be to protect our offspring, even at the expense of ourselves, so we commonly see parents sacrificing themselves for children, in many different species.
And that is of course the flow in Stross's argument about there not being any reason not to colonise. Sure, you can't be on multiple planets, but your offspring certainly can be, so if one of those planets goes up in smoke, your genes will continue on through your children on other planets...
What affects you is having children before you retire, because then you'll be fed and survive a lot more than otherwise. Evolution is a conclusion of that, not the other way around.