Like most technology, it flows from the rich to the poor eventually as it becomes cheaper. The important part you omitted is that it leaves the rest in a worse relative state. Their absolute state is no worse, and likely better.
Arguing against a backup for civilization (or more appropriately, a backup for the species) because it will be used by the rich is like arguing against a cure for cancer because the rich will benefit before anyone else. In the end, a cure existing still drastically increases the chance the poor might be able to make use of it, from zero to some non-zero amount.
This is all also ignoring the fact that when it comes to species level propagation and survival, I would rather Hitler and his closest Nazi associates makes it off world sustainably in the event of a species level disaster than nobody. My commitment to making sure Humanity survives is much more than my commitment to ensuring we are a caring and accepting civilization. We can rediscover valuing life, but once we're gone, the chances we are coming back are essentially nil.