To the extent that scientific knowledge is intrinsically interesting to us, the knowledge of how our brains work is probably the most interesting topic to study. To the extent that technology is useful to us, intelligent machines are probably the most useful technology to develop.
I have been meaning to write up a more detailed justification of this answer, but now I don't have to, because I just read this great paper... "Ethical Issues in Advanced Artificial Intelligence," by Nick Bostrom. I think this paper provides a clear explanation for developing intelligent machines. It touches on all the important issues, in my opinion.
A few points really resonated with me. Here are some succinct excerpts:
- "Superintelligence may be the last invention humans ever need to make."
- "Artificial intellects need not have humanlike motives."
- "If a superintelligence starts out with a friendly top goal, however, then it can be relied on to stay friendly, or at least not to deliberately rid itself of its friendliness."