> but wouldn't you say any process that involves the killing of organisms generally invokes moral questions?

No. The key word is "any" and morality is not universal nor always appropriate. 90% of the world doesn't have a single moral question about swatting a mosquito, and almost no Vegan feels the need to ponder the morality of killing kilogram after kilogram of plant matter or harvesting millions upon millions of yeasts for a single meal, or ponder the holocaust of deaths they cause through the simple act of breathing.

Basic life processes are not moral or immoral. Drawing a circle around one and claiming it's some grand moral issue is silliness.

For example, follow me on this alternate reality philosophical thought experiment. You have to breathe, yet we kill millions of microscopic organisms with every breath, we diminish global O2 availability for our fellow Oxygen breathers, we each increase CO2 by about a kg per day (over 7 billion kg per day or over 2.5 trillion metric tons per year for all of humanity!) further exacerbating global climate problems, and on and on and on.

This is a more important moral question than what we eat. We can always grow new plants and animals to replace the ones we've eaten, but our atmosphere is finite.

Our breath is detrimental to each other and it is our personal responsibility to do whatever it takes to minimize our breathing and maximize the availability of Oxygen to our fellow living creatures: we must minimize movement, sleep as often as possible, avoid cardiovascular exercises, come up with diets that either reduce O2 absorption or reduce Carbon exhaustion, and so on.

Among "Sippers" as we're going to come to be called, heated debates break out whether suicide is a good O2 maximizing choice or not since it will end all breathing. Opposing arguments center around the increase in animal activity as the body decomposes which would bring further imbalance to the atmosphere. Radical Sippers will stage walk-in protests at health clubs and jogging trails to keep people from the immoral acts of cardiovascular exercise. Health forums will be full of angry fellow Sippers trying to turn people away from the ghastly "Nazi"-like organizations called "Jazzercize" and other similar immoral activities "breathers" do.

At the extremes, the "Ethical Atmosphere Users" (EAU) will become a potent and radical organization seeking to stop uncaring breathers wherever they can, marathons, public parks and pools, lamaze classes, sometimes with shenanigans sometimes with violence. We'll go through a dark period where an ultra-militant splinter group of the EAU called "The Inhalers" will bomb a handful of health clubs after hours. The accidental death of a treadmill repair person working late will bring swift police action and put an end to group. Years later, a calmer, gentler ex-Inhaler will recount his troubled youth after becoming a national radio news announcer and promote tree planting and phytoplankton cultivation in personal ponds as a saner, safer alternative.

Entire libraries of Sipper literature will be written focusing on the time-graph [1] of global O2 Content in Earth's atmosphere, pointing out the responsibility of each of us to ensure as much Oxygen for the next creature as possible and how over the last 100 million years the global O2 percentage appears to have gone down and how, when we look in the fossil record during times of high Oxygen content, we find flying insects the size of Eagles...proof that Sipping is the only moral life choice for all people of conscience. That time series graph will become a de facto symbol of the international Sipper movement.

A different hard-line faction will splinter off and rebadge themselves "Sippists" and claim that any unnecessary breathing is deeply immoral and that Sippers don't go far enough. They insist that a minimum of 16 hours a day of sleep is required to minimize personal O2 consumption and that people of good moral principle should be sleeping round the clock. They organize hibernation retreats where groups of Sippists will rent a mountain cabin and take sleeping pills and sleep as much as is biologically possible in order to absolutely minimize their breathing.

A handful of post-child Sippists have been sleeping since 1982 when the "Group of 12" started the "Eternal Slumber" movement. Posters of the group's leader, nicknamed "Sandman" and one of his followers "Rip" can be found in every Sippist center and most of the community Sipper co-ops around the world.

Clearly this is a silly example, the truth is that morality has nothing to do with breathing. It's not applicable and is irrelevant. The same for eating. There are of course moral consideration about what you provide for others to breathe (no poison!) and about how you provide yourself with food to eat, but what you eat in and of itself has no moral quality whatsoever and I'd go so far as to say that attempting to apply morality to eating is foolish from the start.