You are, of course, correct. I know a chap who is a cabbie and he is lovely.
My hackles get raised when I see such stupidity on a taxi forum, but I am assuming that all the cabbies who would be appalled at such an attitude stay away from such sites.
I have, on occasion, been the subject of some anti-social behaviour by cab drivers. Normally buzzing past far too close when the lane next is free or the standard hang off the back wheel in the bus lane trick.
The problem (as Reg knows better than me) is that, in my opinion, the people who "regulate" cabbies and deal with complaints are loath to do anything especially if the complainant isn't a passenger. Complaints on the forum are dealt with a throw-it-in-the-bin mentality, which may be bravado but may also point to the toothless nature of the investigations. So it may that your cabbie with an ipad fixation isn't likely to throw away his livelihood because it is vanishingly unlikely anyone will do anything about it.