The fact that this thread has even gotten to 2 pages in length indicates that pprune is now pretty much ruled by enthusiasts and armchair experts ... and muppets that actually believe what they read in the daily mail.
The airline pays us a great deal of money to operate their aircraft in accordance with the rules outlined in the law and in the ops manuals. End of story. Except in certain well defined emergency cases we do NOT have carte blanche to operate outside the rules - and even then, if we do we had better be prepared to provide a damn good reason for it afterwards.
The daily mail's basic reason for existence is to cook up 50 pages a day of manufactured 'political correctness' outrages because the British Public love to be outraged by stories of political correctness gone mad. Looks to me like the truth here is a lot more mundane, some punter has pitched up with two kids and a car seat that won't fit in the seat. She's in clear breach of the conditions of boarding but expects to be accommodated nevertheless even though that means the crew have to go outside the clearly defined parameters of the rules - which have nothing whatsoever to do with child molesting and everything to do with pax safety in the event of an evacuation. In accordance with SOP, the passenger is duly denied boarding. Well woop de doo, I'm sorry but where's the story in that?