Agnosticism IS the most dishonest position

[The Grand Nudger]

I'll repeat once again, and hopefully for the last time: right and wrong are undefined with the absence of god or some external "ultimate judge" that gives them meaning.

That's quite the claim.  It's not as though a god needs to be present for something to be defined.  Being generous, gods may or may not exist, but we certainly do..and we define things.  Similarly, we exist and judge.  

Is your objection to humans being able to judge and define things, or that our definitions are wrong? 

Is rape wrong? Everyone, atheist or theist, will say it is. Meanwhile, I find Peter Singer, a sophisticated moral philosopher, who thinks it's okay to rape disabled people.

I guess that's one reason to be glad that I'm not Peter Singer?   

Now let's listen to the guy's wise reasoning : “When the death of a disabled infant will lead to the birth of another infant with better prospects of a happy life, the total amount of happiness will be greater if the disabled infant is killed. The loss of happy life for the first infant is outweighed by the gain of a happier life for the second. Therefore, if killing the haemophiliac infant has no adverse effect on others, it would, according to the total view, be right to kill him.”

You read that right : it's okay to kill the haemophiliac infant. And he gave a sound utilitarian argument for this position.

I am not arguing from authority here, or implying that atheists should advocate for the same ideas, but I think that this guy demonstrates that we can philosophize any moral position to the realm of acceptable if we don't have some ultimate reference.

If you read carefully, you might see that the above does have an "ultimate reference" - total amount of happiness.  I agree with you here, though.  It's true that different rational products will follow from different moral systems, and that a moral system can be reverse engineered to justify any action.  

Again, right and wrong are red herring in this context. I agree we all have this inherent moral compass that prevents us from allowing such stuff. But this inherent morality in itself warrants an explanation.

What inherent moral compass?  You're unwilling to state that skullfucking your neighbors' kid would be wrong in a world without a god.  It doesn't sound, to me, like you have one.  You believe..instead, that things are only right or wrong insomuch as a god is in or out of the room.