An attempt at a simple, two-rule morality

I've been thinking about morality recently. Plenty of people claim to offer moral systems, but as a modern, relatively enlightened individual most of them seem to include relatively arbitrary injunctions, and as a geek most of them seem both over-complicated and over-specified, and yet still riddled with unhandled edge-cases.

Take the Ten Commandments, for example:

1. I am the Lord your God
2. You shall have no other gods before me/You shall not make for yourself an idol
3. You shall not make wrongful use of the name of your God
4. Remember the Sabbath and keep it holy
5. Honor your father and mother
6. You shall not murder
7. You shall not commit adultery
8. You shall not steal
9. You shall not bear false witness against your neighbor
10. You shall not covet your neighbour's wife/You shall not covet anything that belongs to your neighbour

As a modern weak atheist there seem to be some obvious errors or redundancies there:

• The first two injunctions presuppose a belief in supernatural entity, so as someone who finds no rational reason to believe in a supernatural entity, these seem suspect or redundant. Firstly they could be better summarised as "Do not believe in any gods other than me". Secondly, unless God can himself demonstrate his moral authority (instead of, as most religions do, simply assuming it) they seem more concerned with promoting and propagating one religion than with laying down universal moral rules to live by.
• The latter half of the Second Commandment seems to contradict the First Commandment and the first half of the Second. As a non-Christian, I would define an idol as an entity which is worshipped blindly and absolutely. This definitely includes the Christian God. Alternatively, one can take the assumed definition in context as "anything other than the Christian God"; but then (as above) it amounts to an empty re-iteration of the first commandment-and-a-half, which themselves rely on the undemonstrated assumption that the Christian God is an absolute moral authority.
• The third again seems unnecessary - why should a system of morality define it as immoral to take the name of its creator in vain? A system of morality should stand up on its own to reasonable argument, and defining veneration of its creator as a moral requirement frankly sounds far too much like begging the question.
• The fourth is simply redundant - why should a moral system concern itself with keeping a day of the week specifically marked out? Admittedly there may be some social benefits to setting aside a whole day of the week for adherents to remember and reflect upon their moral choices, but I don't see why such an injunction is morally good, rather than simply a good idea.
• The fifth is again a good idea, but too over-simplified and prone to edge-cases. Sure honouring your parents is good for social stability, but what if your father is a deadbeat dad and your mother a shiftless crackhead? This commandment smacks entirely too much of the kind of unconditional, assumed authority that typifies the Ten Commandments, and is far too incomplete to serve as a good rule. Moreover, why should parents get special treatment? Why not simply honour anyone who is wiser, more intelligent or more experienced than you?
• The sixth through ninth are pretty good, prohibiting murder, adultery, theft and lying. However, you have to be careful with definitions - for example, distinguishing between "murder" and "killing", which may include self-defence or defence of a third party). Moreover, I can't help wonder if these are overly specific, leaving out whole classes of immoral behaviour not explicitly prohibited. Take "dropping litter in public", for example - most of us would agree that it's a comparatively moral issue, and yet it's not covered by these four injunctions.
• Leaving aside the implication that a wife is a possession to be owned, the tenth is again pretty good - I've always understood this as an injunction to try not to feel jealousy (because it's frequently a sterile, unproductive emotion), but rather to concentrate on bettering your own life and resist the temptation to waste it wishing you had someone else's.

Clearly, then, there's a lot of fat that could be cut, and a lot of edge-cases to handle.

Instead, I present my best stab at a moral system. It's only two injunctions:

1. Do unto others as you would have them do unto you, at the highest level of abstraction possible.
2. Always seek to minimise harm in the long run.

There are a couple of subtle but key points here.

"Do unto others as you would have them do unto you" is a pretty good moral system on its own, but the addition of "at the highest level of abstraction possible" removes edge-cases and makes it a lot more specific and defensible.

For example, it would now prohibit a masochist excusing undesired violence against others on the basis that he liked to receive violence himself. Rather, he is now constrained to consider their wishes when deciding whether it's acceptable to hurt others, rather than simply the shallow fact of his actions.

The second injunction is a somewhat Utilitarian attempt to minimise the total amount of harm in the world (where we define harm in the usual way, as "physical or mental damage").

This prohibits short-termism in decision-making (which often merely saves up problems or harm for later, possibly even increasing the total amount of harm).

It also allows for harm to be caused where necessary, but only where such harm is in the service of preventing greater harm - this would permit otherwise difficult moral choices, such as the hypothetical "killing a single child to prevent a nuclear weapon going off in a major city".

More trivially, it also permits things like "contradicting someone you believe is incorrect", but when considered in conjunction with the first, only if you're happy being contradicted or corrected by others in turn. It also effectively prohibits you from debating others' positions unless you're equally willing to give their arguments due consideration.

So that's it. The first injunction prohibits most non-victimless crimes, because we would all rather not be the victim of them, and the second permits harm to come to others, but only if we can reasonably assert that it will prevent greater harm elsewhere, or in the future.

With a little reasoning, as far as I can tell, every action or injunction we can reasonable justify as "moral" seems to be derived from these two principles.