Morality

[vulcanlogician]

"Is seen with an effort"...? Is Plato referring to the "effort" it takes to believe a dogma when it is presented to you? Or is he referring to something else?

No, he’s referring to the effort to see The Good. And by this he doesn’t mean, that it takes such effort to see what’s right, but  the ultimate root, or source of such perception. Our perception of what’s right, is like seeing light from the sun, but not the sun itself, it takes considerable effort to see the sun.

“. It cannot be clearly seen or explained, but once it is recognized, it is the form that allows one to realize all the other forms.”

So, if you accept Plato's bit of wisdom here, then you may want to rethink the idea that only theists can be moral realists. 

Atheists can recognize the Good as well as any believer can. Some things might even work in the atheist's favor in trying to recognize the Good, such as not being bewildered by dogma. An atheist can search for the Good armed with only a sincere heart and mind. At the very least, I will say that an atheist is at no disadvantage when trying to distinguish the good from the not good. At the very least, they are just as able to distinguish an objective morality as a believer.

Edit: Since you also seem confused about what an atheist might consider moral facts, here is an argument I've put forth here before (from a paper found in the disclosed link):

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(1) A property P is genuine if it figures ineliminably in a good explanation of observed
phenomena.
(2) Moral properties figure ineliminably in good explanations of observed phenomena.
Therefore
(3) Moral properties are genuine.

The ability of putative moral properties to feature in good explanations is one perennially attractive argument in favour of the metaphysical claims of realism. The initially attractive thought is that moral properties earn their ontological rights in the same way as the metaphysically unproblematic properties of the natural and social sciences, namely by figuring in good explanatory theories. So just as, for example, a physicist may explain why an oil droplet stays suspended in an electro-magnetic field by citing its charge, or a social scientist may explain high levels of mental illness by citing income inequality, a ‘moral scientist’ may explain the growth of political protest movements or social instability by citing injustice. Likewise, just as an observer of the physicist may explain why he believes that the oil droplet is charged by citing the charge itself, and an observer of the sociologist may explain why she believes that income inequality exists by citing the inequality itself, an observer of the ‘moral scientist’ may explain why they believe that a situation is unjust by citing the injustice itself. In such cases, it appears that the instantiation of a moral property – injustice – is causally relevant in producing an effect – a political protest movement or moral judgement.

http://eprints.nottingham.ac.uk/1930/1/T...prints.pdf

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