Manure at Ramsay's

Gordon Ramsay has had a pile of manure dumped outside his restaurant in protest at his liking for (and cooking of) horse meat burgers for a TV programme. Whilst my first reaction was to think of other 'celebrity chefs' who might benefit from a similar treatment (naughty of me, I know) - I did wonder what the objective difference between horse and cow meat is, or horse and lamb etc.

If the argument is that 'all meat is murder', it's extreme but self consistent (as long as the proclaimer realises the hypocrisy should they ever need medical treatment) - however, if the argument is 'you can cook a cow, but not a horse', then I don't understand in any objective way.

It's not that I'd love to eat horse, I don't think I would (though Kangaroo used to be sold at Tesco, it was tasty). I just don't understand the objective difference between that and beef, the difference which makes one acceptable and the other wrong.