You’d think that in Britain, the worst thing that could happen to you after sending a few critical WhatsApp messages would be a passive-aggressive reply or, at most, a snooty whisper campaign. What you probably wouldn’t expect is to have six police officers show up on your doorstep like they’re hunting down a cartel. But that’s precisely what happened to Maxie Allen and Rosalind Levine — two parents whose great offense was asking some mildly inconvenient questions about how their daughter’s school planned to replace its retiring principal.