Shadow, we're now not on a motorway but on a circuit: as was pointed out quite reasonably, there's no NEED for any horse trailers or boxes on roads, either, since all horse-related events are purely for leisure and pleasure, and usually for the well-heeled, too. You'll be moaning about ambulances next, because they've usually got people on board who've been stupid enough to have an accident or are too old to be of much use, anyway.
Caravans are taking people, many of whom will be workers, on much-needed breaks, so that they can return to their work refreshed and happy. Who knows - they might even be in jobs which have some social purpose, too, rather than just propping up another way of relieving people of their cash? And yes, that was a dig!
If you're going to start trying to base transportation on its moral worth, then look at who drives cars and for what purpose? A big 4x4 with black windows, rushing the latest imported cocaine to a bunch of overpaid stock exchange yuppies? A Lamborghini, of no community worth whatsoever, simply there to play to the vanity of its rich driver? A Picasso which is driven by a wife-beating alcoholic? Hmm... nope, don't quite see your argument for 'worthy' vehicles standing up. I'd give up now, before we're reduced to bicycles, but only if we can prove they're an absolute necessity to the good of mankind.