JoJo said:
And humans? If you aren't picking and choosing between organisms, no reason to leave
Homo sapiens off the menu
Arguably, treating a brainless jellyfish and a sentient pig as if they are equal is itself an attempt to cope with the reality of life, by justifying that you have to eat to live and so it doesn't matter what you eat. This line of thinking clearly doesn't make sense, for example lets say you are driving a train carrying hundreds of people. You find to your horror that on your present track there are five people trapped with no way to get out in time, and on the only alternative track you can take, one person is trapped. There is no time to stop and clearly choosing to steer your train off the tracks and killing hundreds is not an option. You must take someone's life to live but surely the moral choice is to choose the option that causes least harm: i.e. the track with just one person trapped? Does that make sense?
We, as modern men, live in an incredibly privileged state, but when people find themselves under prolonged starvation this taboo will seem more and more flexible with each passing day. I need not testify for this - history does that better than I ever could.
Seeing all living things as one whole collective comes first - sentience is an imaginary line drawn to divide these living things, and is deeply secondary. Sentient beings, in effect, are given preferential treatment. And what a surprise that is, that we, humans, who created this divide, place ourselves squarely in this "superior" group. How fortuitous indeed! Strictly speaking,we should not be allowed to judge ourselves to be sentient, and thus reap benefits from it, for we have vested interest in saying so. Personally, I think that flesh-eating bacteria should have the honor of deciding who is OK to eat and who is not.
In your example, you've created a set of specific circumstances that guide me to a particular choice(though, if I were to take a truly purest ultramoralist stance, I would go for "none of the above" answer and absolve myself of choice by just flipping a coin, thus avoiding staining my hands entirely - I do delight in sophistry).
In every situation in the actual world it would have a set of circumstances that would affect my choices. So, situation when it TRULY doesn't matter what you eat, is a purely hypothetical construct and does not really exist in the real world. In the confines of the mind one ought to do whatever he/she pleases, question is how it all manifests itself - real world is the only place where this matters. In practical terms, there are always swaths of various circumstances that dictate this choice.
Having said that...
Principle is inviolable; it's manifestation is flexible due to considerations of practicality.
Also, my view of treating all things the as equal is more simple and streamlined, which is a mark of elegance. Elegance is beautiful. And I am nothing, if not a disciple of the Beautiful. :3