(THIS IS NOT MEANT TO BE A CONTROVERSIAL POSTING, please play nice!)
Do you tell guests, when you use an ingredient that they may not like (I'm not talking about health-related or religious restrictions; I believe these should be respected)?
Or do you go quietly ahead, knowing that your guests are very likely to enjoy the dish, if they don't know that something a bit out of the ordinary is present in their food?
I'm not talking about the intent to trick guests into eating something, by the way.
In my post about using a pinch of tobacco to flavour chocolate truffles, dbcurrie raised the very valid point of considering guests' preferences.
The thing is, how far do you take take this?
When we prepare food that goes beyond 'just fill 'em up' (a meal prepared for others is is usually intended to be at least a bit beyond the ordinary), at what point does our judgement of the best choice conflict with accommodating guests?
I know, for example, that the presence of dairy products in savoury dishes makes them as inedible to me as the contents of a spittoon, but if there IS dairy in such a dish, and I can't tell, I don't want to be enlightened. I know my attitude is purely psychological, and there are probably many things I would miss out on, if I were informed, out of courtesy, that they contained milk, cream, yoghurt, etc.
Your turn: What are the ethics involved in telling guests precisely what is in their food, and what determines this?