The highest purpose of any technology, whether microblogging or semiconductor fabrication equipment, is to improve human lives.

One can make arguments on both sides about whether Facebook and Twitter are net positives or net negatives on society. However, given the sheer scale of their userbases, and the amount of those users' time they choose to spend on these services, if FB/Twitter usage is even mildly positive in net impact, the total impact dwarfs other more "hardcore" technology products.