A Measurable Morality I had a very similar idea about existence itself being good, but from a totally different argument. I like the original post, because it does seem to objectively prove (if we treat a "reason" as being "something", and assume noncontradiction) that morality cannot exist if there is no existence. My proof just shows that it's possible to believe that existence is good without contradiction.
I started the proof with the a thought experiment: What would the moral value of the Earth be if all life on it died? It seemed to me that the obvious answer would be that it would have about the same value as Mars, whatever it's value is. But it does not seem to me that Mars is evil.
If we assume that existence is good, then bad can only be the loss of existence (such as how murder is bad because it takes away the life of a man, which is good). In this case, God can't take anything from us which he didn't give us first. We cannot be killed until we have first lived. We cannot lose our health until we had it first. If pain signals the loss of health (which it usually does, since this seems to be its purpose), then we cannot feel pain unless we have first had health. From this line of thought, it makes eternal torture seem like a strange idea, because if you felt pain continually without losing all your health and dying, then it means that that pain is meaningless. I suppose if God did create a place where we could be tortured indefinitely without dying, that would be a very strange and bad thing.
Anyway, if a person can accept that nothing is not evil, and his bad circumstances are not worse than a meteor destroying all life on Earth, then it must follow that his circumstances are on the net good. What appears to be very bad is actually just the change from good to less good.
In Genesis, it said that every time God created something, he said it was, "good." So, I think people have been wrestling with this idea for a very long time.
I typically think of values as being arbitrarily asserted, so, it is more natural for me to make the claim, "It is possible to claim that existence is net good without contradiction," than to prove, like you appear to have done, that existence must be good if morality exists at all.
I have 2 more similar arguments: It appears that only living beings have the experience of "good" and "bad" (this observation is so fundamental, you might actually define life as being those things which have preferences). So, if we want our values to have an affect on the material world, then we must limit our morality to the actions of living beings. It could have an effect, for instance, if I teach my daughter not to steal. It will have no effect whatever if I said the same thing to a rock.
The second argument comes from evolution/game theory. It seems to be necessarily true that those moralities which are good at propagating themselves will become more common, and those that are less good will not propagate themselves. I like to call this "God's morality", because assuming that God made the world the way he likes, then God likes moral beings to try to propagate themselves and their morality. This is the morality that WILL BE.
Technically speaking, the is-ought dilemma still holds, so that these observations are only objectively moral if we assume that we want our morality to have an effect on the material world, and if we like for our morality to not be self-defeating.
The second argument leads me to the idea that morality is enlightened self-interest. I am composed of several parts, including a body, mind, and "heart". I am also a cell within a social body, and I am incapable of propagating myself into the distant future by myself. So, it makes sense that I ought to take care of each of my parts: take care of my bodily health, educate my mind, try to find (or assert) the good, try to do good to my social unit, etc. This train of thought leads roughly to the standard morality that most people would recognize.