I see this must be why some people keep thinking I’m taking about the Christian deity. I capitalized the “g” in the title because it is a title. I did not intend to make any statement on the Christian god, though, I do not believe that deity exists.
This is of course part of the problem. We tend to believe that no other God is even possible. Some attributes of God we can learn without recourse to revelation, and I think these are the ones we’ve tried, for the most part, to use when discussing this. Part of the argument is covered by Acquinas here:
newadvent.org/summa/1005.htm. (It links up with the rest of what he says elsewhere, but it can all be found from that site.)
The short version, mangled down into something easy to type in one sentence, is that existence and goodness are essentially the same, and as God’s essence is existence, God’s essence is also goodness.
You could deny that existence can be called goodness, I suppose, but I have yet to see a better standard. It does in fact work: Things which we call evil are understood in this way to be things which lack some part of what they need to be complete, or things which do not reach their full potential, as it were. That is, to murder is to end a life before it is complete (but to die of “old age” is the completion of a life and so not evil), sex outside marriage is a failure to allow sex to be what it is fully meant to be (complete self giving, and sign of marital union, etc etc) which of course means that things like rape which reduce sex to even less are even worse (obviously). Torture and the like involves the torturer treating the person like something less than a person, etc.
It requires, of course, that you know (or are able to figure out) what things are meant to be, but any standard of morality must have a similar requirement - a standard is a standard, something which is set and is what it is by virtue of being itself. Something is a meter long because if you measure it against a meter stick, you get one meter, but the (perfect, absolute, quintessential) meter stick is a meter long purely because it is a meter stick sort of thing. Note that I am not here arguing that our standard is better (since that’d be off topic), only that attacking it because it needs assumptions attacks all standards - including any that say that God is bad.
As a last point, I want mention that the problem of evil is not really a problem, it’s just a lack of knowledge. That is, when you ask why a good God would allow evil and fail to get an answer you like, that is not the same as saying there is no answer (and the arguments that say there cannot be an answer all fail, as they assume that omnibenevolence equates to the desire and willingness to actively repress all evil, which is hard to demonstrate in any way other than saying that that is what you mean by the word). It may be that on an intuitive level, some people (although not myself, that particular issue has never really bothered me very much) think that refraining from preventing evil must always be evil, but frankly that doesn’t really mean much (and is demonstrably not believed very strongly, since we refuse to outlaw and thus attempt to prevent many things which are evil and do not view this refusal as a bad thing).