A person's life is far more than just how they start out. Many people have started in situations like this and have gone on to have wonderful lives. Many have even changed the world. This alone isn't enough to convince me that we should give in to short-sightedness by allowing people to prevent or destroy future human lives.
"In any case, if people can choose whether they want to have a child or not, then contraception just helps them make that choice."
In the same way that it's smart to invest money long-term, I think it's smart to invest in long-term human potential. I think that's really our greatest resource.
EDIT: added a little tact