I don't hate them, but I would say they are ridiculous in the same sense that we "need" cars to be prosthetic extensions of our bodies because we (speaking generally of people) are too pathetic to get around using our own muscles.

What advantage does a segway have over a bicycle, other than appealing to those folks to whom even the wonderfully-efficient mode of transport we all know as cycling is too difficult?

With all that being said, (1) I don't claim to be an expert, because I've never used one of these things, and (2) I realize that they may make sense in limited applications such as for some urban police.

Though I'd rather see folks on segways than in cars.