Well, their reasoning may be faulty, but I'm not entirely sure the result is wrong. In my opinion, computers should be avoided (in schools) when the teachers have no idea what they're doing or how they're doing it. There's so much technology in schools when a simple blackboard would get the job done and save more time. Most elementary teachers don't have the time or interest to learn enough technology to keep up with the changes from year to year. Don't get me wrong, I'm all for kids having access to computers. I'd just like for them to be able to get their questions answered or get real help when they run into a problem.
Steiner's esoteric views are hardly a part of the day to day discussion at any Waldorf scool.
Rather (from Wikipedia):
"Waldorf kindergarten and lower grades generally discourage pupils' use of electronic media such as television and computers.[38] There are a variety of reasons for this: use of these is understood to conflict with young children's developmental needs,[50] media users tend to be physically inactive, and these media often contain inappropriate or undesirable content which may hamper rather than exercise the imagination."