I went to a panel at Worldcon on the morality of generation ships, and have been thinking about it since.
(I'm also going to take this opportunity to recommend this Jo Walton story set on a generation ship, which is great and has something to say about choice and decisions.)
So, the question under discussion at the panel was: is it morally acceptable to board a generation ship (i.e. a ship that people will live on for multiple generations on their way to another planet), given that you are not just making a decision for yourself, but for your future children, grandchildren, etc etc. The two main categories of moral problem that the panel identified were:
- the risk of the voyage itself;
- the lack of choice for every generation after the one that gets on the ship in the first place.
The 'risk' issue seems reasonably strong. It's very unlikely that anyone would have a really clear idea of what the planet was like that they were going to. If you're using a generation ship at all, then you probably don't have any other form of fast travel, so any information that exists about the planet will be scanty, very out of date, or most likely both. (See Kim Stanley Robinson's Aurora, which is also great.) So it's not at all a reliable bet that your descendants will truly be able to settle where they're headed to, even if it looks good from here.
There are also the risks of the voyage itself, including but not limited to radiation issues, the possibility of running into something else, and the likelihood that the ship will genuinely be able to maintain a workable ecological system. We don't have good on-Earth comparisons for small closed systems; what experiments have been conducted have been very short-term and not terribly promising. What about the social dynamics? What are the risks of, say, a totalitarian system arising? If the risks on Earth are very high, or humans on Earth are facing imminent disaster, then this might be an acceptable trade-off, but how high is 'very high' and how disastrous does a disaster have to be? Does it need to be Earth-wide? If your current home is, for example, sinking under rising waters, and you know that any alternative will mean becoming a refugee in poor circumstances -- how much risk is 'reasonable' to accept then?
Which brings us on to the issue of 'choice'. One could argue that a kid living in a refugee camp without enough food or warm clothes has, notionally, some future 'choice' or 'opportunity' to escape that. A child on a generation ship is stuck there.
But why is "can't leave generation ship" morally different from "can't leave Earth"? Which is of course a situation into which all children are currently born and which we do not consider morally problematic. And how realistic is the 'choice' that the average Earth-born child has? This was where I thought that the Worldcon panel fell down a bit. They threw the word "choice" around a lot but didn't at all interrogate what realistic "choice" is available to which children in which situation on Earth. There are many kids born without very many realistic 'choices'; children who are unlikely to go more than a few miles beyond where they were born, children whose projected lifespan is short, children whose lives are likely to be very difficult. How different is that, in reality, from a generation ship? In fact, if the generation ship does work, it might be a better life than on Earth: guaranteed food, shelter, and useful work (making the ship run).
The panel talked about limiting the choices of children born on the moon, because they might not be able to go back and live on Earth -- but why is Earth necessarily better than the moon, or Mars, or the asteroid belt? Why isn't it immoral of us to have children who are stuck down here in the gravity well?
More generally: we're constantly making choices for our children, and through them for generations beyond; we're constantly giving them some chances and removing other options, every decision we make. Is that immoral? It's not avoidable, however much privilege you have, although most certainly more privilege generally means more options.
Would I get on a generation ship? Well. Not without a really good perusal of the specs. But I'm not convinced that it's immoral to do so.