Don't get me wrong - Objectivism has a lot of non sequiturs that just leave me scratching my head. I am drawn to the positive observations Objectivism makes as its premises, but by the time they get to their normative claims, they don't really follow at all from their premises. But I like Objectivism because at least it makes a concerted effort to only adopt as its premises positive claims that have been clearly demonstrated in science. UU makes normative claims about human nature in its very premises which as far as I can tell come strictly from the humanities or aesthetics, all of which are subjective. It's not quite as robust as people seem to think - it's actually quite easy to make very sensible normative claims when you actually started out with normative premises. It's self-congratulatory. It also makes it easily corrupted when applied to real life social systems, IMO, and we need something better if it's to be more useful than just a mental exercise.

Having recognized the problem, please help us correct it.

would say that sciences such as economics and biology line up closer to Objectivism in their approach. Economic models traditionally only needed to account for selfish actions. The Ricardian theory of Comparative Advantage is an example. Darwin as well did not rely on altruism to describe natural processes. Neither did Dawkins in The Selfish Gene.

What relevance does any of this have to which ethical system is preferable?

Both UU and Objectivism have insights and thinkers in both frameworks have advanced atheist thinking in general. Some of the most elegant refutations of religion I have ever read were written by Objectivists.

I would say that sciences such as economics and biology line up closer to Objectivism in their approach. Economic models traditionally only needed to account for selfish actions. The Ricardian theory of Comparative Advantage is an example. Darwin as well did not rely on altruism to describe natural processes. Neither did Dawkins in The Selfish Gene. I do agree with the Objectivist critique of UU, what they call the error of frozen abstraction. UU does take altruism a little too far and substitutes it for ethics itself - as if without altruism, it's not ethics. Perhaps that's why you fail to recognize Objectivism as a philosophy of many atheists? Objectivsts after a certain point start to go off the deep end with Libertarian economic ideals, tin foil hats, and perpetual motion machines.

I'm quite happier with the "coldness" of Darwinism over UU and the "selfishness" of economics (real economics that account externalities and public goods, which Objectivists seem to run from) over Objectivism.

Just a little remark to nag you... but Universal Utilitarianism isn't the basis of atheist morality, just one of many options. Not judging which one is better or worse, but for example Objectivism is another valid alternative that some atheists subscribe to. Meanwhile I don't fall into either one because I'm not satisfied with either philosophy.

Objectivism fails for a number of reasons: even on the level of personal self-interest it fails because it dictates the wrong choice in "prisoner's dilemma" type situations. Additionally, it would arguably require a superhuman degree of foresight to apply it in a way that would create a stable and functional society, and applying it in that way would arguably be tantamount to adopting some form of Utilitarianism for purely selfish reasons.

As for Universal Utilitarianism, perhaps you should tell Adam why you aren't satisfied with it?