What is the difference between eating a guinea pig and eating a big mac?

[Flatulent Hermit of Lindisfarne]

I ask because the TV presenter Phillip Schofield has been bombarded on twitter with angry fans complaining that he had eaten a "pet", Schofield had been in another country where it's normal to eat a guinea pig.

Anyway, a lot of people who complain about him eating a "pet" eat big macs, why do they think it's OK to eat burgers but not guinea pigs?
@ Four Legs Good - I think cows are cute too, they are totally innocent, just eating grass and not other animals, poor cows.