This seems like a rabbit whole, at some point there's no objective ethics, you pick your line. Are you going to include bacteria, yeast, common viruses, dust mites, there's plenty to choose from. I think one thing that seems relevant to humans, is we seem to be bothered only once we can relate to the other being in a more explicit way. This is true even between our peers. Maybe as we understand more and more of other…
Speaking of yeasts, I guess it's not something that's on everyone's minds, but the reason bread rises is because yeasts die in the heat of the oven and, reacting to the deadly environmental conditions, radically increase their rate of fermentation of the carbohydrates in the dough thus releasing abnormally large amounts of CO2 in a very short time. Essentially, bread rises because of the the death throes of tiny, mic…
My impression was that fermentation outside the oven causes most of the rising, with a bit of "oven spring" from the vaporization of water in the dough.
The yeast obviously die in the oven, but I don't think the death per se is critical for the leavening.