It's because people like simple solutions
I actually work in a school (see caveat at end), with wireless networking, so I'm quite interested in this one. I think what actually lies at the root of this is that people want a nice clear 'solution' to problems - there are a lot of kids with behavioural problems (and no, sorry but a 'smack in the arse' is not a solution, as one poster suggested) but these are likely to be due to a multitude of causes acting in concert or alone.
Factors such as society, the composition of the family, type of leisure time, diet, political climate, or methods of education are almost all playing a part in changing the way children act and think, as they have done for years. However that's scary because it means that we can't wave some magic wand and create the children that we think children ought to be; one of the reasons I'd hate to be anything other than a school network manager is that kids are so wonderfully challenging to all your ideas and prejudices, they're FUN to work with.
Right now it's wi-fi because that has the added attraction of being some mystical force in the ether to which can be attributed the changes in society we don't like. On the other side of the coin wi-fi is going to allow teachers to create exciting and innovative lessons which will shape our children for years to come; but hey let's not focus on the positive here.
I agree that the possible health effects of wi-fi should be monitored by professionals in a rational and scientific manner, but so should everything else in the school environment. Furthermore if there are students who are proven to suffer ill-effects from wireless networking (as in the case of the poster who is suffering effects from his games console) then measures must be taken to accommodate them, the same way we accommodate students with a whole range of other special needs in the school community.
But to blame wi-fi for some perceived decline in behaviour with little evidence to back it up would be a disservice to our students - after all they'll have to operate in a wireless-rich environment when they get jobs, would it be fair to say that they shouldn't learn this in schools?
(please note, these are my own personal views and should not be taken to represent the views of the school where I work, or of the education community as a whole)