A gene is happy to sacrifice the genes of other individuals - it is not happy to sacrifice copies of itself, no matter where they are found. Hence we tend to protect mammals more than reptiles, apes more than other mammals, humans more than other apes, our own countrymen rather than those from other countries, and our family more than others from our country.
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...
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...