Why bother, even if there is no life there now that doesn't mean their won't be when we finally arrive. Or contrary if there is life there now that doesn't mean it will survive until we get there.
The odds that there is life on our generational ship when we arrive are not that great either.
I seem to remember in an Iain M. Banks novel that there was some controversy about terraforming, like there was an other civilisation that considered it an atrocity and hated The Culture fot that?
The odds that there is life on our generational ship when we arrive are not that great either.