Actually, an honest garnish I'm okay with. I've long come to terms with the fact that the purpose of a garnish may be for flavour, or for aesthetic qualities. It can, and often does, provide an element of both. Again, this I'm cool with too. Until, that is, this ambiguity is exploited...
It was lunchtime and I was hungry. I wandered into The Co-op and headed for the 'lunch section'. Now I'm a big fan of Coronation Chicken. The mild curry powder and sweet raisins work together wonderfully, in a way that says, "You've done four hours work, so treat yourself. But don't get carried away. You've still got four hours left."
Suddenly I recoiled in horror. What was going on with that over-sized garnish? Had they taken the Lamb's Lettuce and Green Batavia out of the baguette (where it should've been) and tried to pass it off as a garnish-come-ingredient? Oh god, they had. I can't think of a better way to ruin lunchtime than to insert lettuce along the length of a creamy baguette with my finger, trying to ensure an even distribution.
If you want to add a garnish, add a garnish. Just don't do this.