I'm going to agree that this is a very touchy subject to comment on, but I'm going to give my two cents.
I'm very sympathetic towards any person needing assistance getting around. My grandfather, who just passed away this past April, had Polio since the age of 6 had to end up getting a EVC to get around. My grandmother and aunt both need canes and walkers to get around, and so on and so on.. So, I understand the needs of the physically challenged. And I'm going to find myself there someday (I've played alot of football).
But, as a father of 3 girls, two under the age of three, I wouldn't be happy if one of my girls got hurt because someone used a Segway vs. a EVC or a wheelchair. There is, at this point in time, a far less of a serious injury vs. someone running you over with a Segway. Think how many people have written about getting bumped with a double stroller (sorry to those I may have healed in my trip) and the EVC's now.
Disney provides alternatives for those who need assistance and I personally side with Disney on this one UNTIL Segways can be just a cautious as the wheelchairs and EVC "appear" to be.