I had fun discussing this topic because I think we agreed on most of the starting assumptions. I have restated the core of my argument in light of your comments and added one or two minor additions. This concludes what I want to say for the present.

Common Descent

If there are any facts in science, one of them is common descent of all life from a single simple life form (or a single gene pool). Our biological design is contained in DNA. DNA is a digital data storage system. As we changed from simple to complex life forms over billions of years, we can think of it as moving though a multi-dimensional landscape. Points close together in the landscape represent a small genetic change. All life started at the same point on the landscape and moved to form the millions of species, each occupying a niche. The journey from the start point was a continuous path without breaks (although technically the small steps, being digital, were punctual but generally small). In fact each species, with each individual varying slightly genetically, occupies a small area on the landscape.

Put this another way, all life genetically speaking is related. If we consider genetic distance in the landscape, we are a finite distance from each other human as well as a finite (but larger) distance from all life. All life are literally our cousins (or closer).

Morality and a Slight Tautology

As I said: “Systems of good and evil applies between all the family of life, unless there is a logically valid reason why some part should be excepted.”

You correctly observed: “If you can propose exceptions to the rule, then the rule is not without exception.” Essentially, I stated A or not A.

I would say my statement is, deliberately, a tautology. But in the next line I give the critical context: “Note: I have not yet heard a valid reason why animals and plants should be excepted.” My argument is then: A or not A. Not A is false. Therefore A. My point is “Systems of good and evil applies between all the family of life and no exceptions“.

Now is probably the time to acknowledge that you disagree with my first point in its broadest interpretation.

Application to Human Equality

My second central point is most ethical laws we currently depend on apply only to humans. To quote you “I am sure you would agree with the proposition that I cannot grant a pig the right to vote” in reference to current culture “all humans above age X are allowed to vote”. In light of my first point, this law would be invalid since it discriminates in an arbitrary way.

Therefore all human laws of equality are flawed. Universal equality laws, if they could be devised, would be permissible. I doubt this applies to all ethical systems as long as we accept some discrimination (such as caring for your offspring rather than every living thing – see its not all bad!).

Source of Good and Evil

Two sources of good and evil are the natural behavior (i.e. naturalism) and metaphysics. To quote you again “I do not think that either case can be satisfactorily demonstrated to be analytically true”. What is interesting is the implications of each if we accept my first point (which you don’t).
If naturalism is true, well obviously we are in atheism territory. No surprise.
If metaphysics is true, then metaphysics gave good and evil to all living things – not just humans.

In Defense of Suffering

This is not exactly central to my argument but I wanted to note your point: “it is wrong for all species to unneccessarily suffer, where the avoidance of suffering can be facilitated”

This rule implies a life without suffering is ideal. This is like trying to ban inclement weather! To take any risk, there has to be the possibility of a negative outcome – which in life leads to suffering. This rules out taking great risks. We are condemned to mediocrity.

I imagine you want to refute that :) And the last word (in this post anyway) goes to the Bard – was he being sincere or sarcastic?

What a piece of work is a man!
how noble in reason! how infinite in faculties!
in form and moving how express and admirable!
in action how like an angel!
in apprehension how like a god!
the beauty of the world, the paragon of animals!