In this instance, if as the article states, the passenger in question made a bomb threat to crew, then it seems reasonable for the police to have been involved.
If on the other hand, a passenger is drunk but is sitting in their seat and not causing any particular disruption, it would seem a little harsh for them to be deboarded. I would guess that this kind of thing happens rather often - the business meeting over a very long lunch followed by a taxi to the airport to get the plane home (I've been there myself !)
I haven't read the Highway code in a long time, but seem to recall that walking on a pavement while drunk is technically an offence. As far as I'm aware, if the police see someone walking home while drunk shortly after pub closing time and there are no other factors involved, they usually don't see the need to get involved.