I hope you mean "if they are actually observed".
Yeah, that's it.
But, if we didn't believe (to a degree) in theoretical predictions before making observations to confirm them, then we wouldn't know what observations to attempt, and would almost never actually observe something useful!
The anti-realist doesn't say that we don't believe in theoretical entities. She says that we don't have strong reason to believe in them. I suspect most of us believe in things we don't have strong reason to believe in. It might be an anthropological fact that scientists tend to believe in theoretical entities and use these beliefs as guides to future research. Anti-realists don't want to deny this fact, they want to deny that the scientists' epistemic attitude (prior to making the requisite observations) is justified.
Anchoring on what most humans can observe unaided is just silly. I have acute myopia since age 6; without modern glasses I wouldn't be able to observe the moon in the sky - or to read about any scientific theories. Should I discount them on that account? Or if someone were born with unusually fine eyesight, making them the only person able to observe a tiny mote of dust - should everyone else disbelieve them? If a trained dog barks when he smells explosives, which humans can't smell, should we ignore the dog?
I agree. This is what I was trying to say when I said the distinction between observable and unobservable doesn't make sense. It would be silly to construe "observable" as "observable without technological aids", but once one allows technological aids, where do you draw the line? We have experimental verification of quantum chromodynamics. Why doesn't this count as (extremely indirect and mediated) observation of quarks?
I felt this was a confused question for the reasons you've defined and so I've voted other.
Despite being (IMO) a philosophy blog, many Less Wrongers tend to disparage mainstream philosophy and emphasize the divergence between our beliefs and theirs. But, how different are we really? My intention with this post is to quantify this difference.
The questions I will post as comments to this article are from the 2009 PhilPapers Survey. If you answer "other" on any of the questions, then please reply to that comment in order to elaborate your answer. Later, I'll post another article comparing the answers I obtain from Less Wrongers with those given by the professional philosophers. This should give us some indication about the differences in belief between Less Wrong and mainstream philosophy.
Glossary
analytic-synthetic distinction, A-theory and B-theory, atheism, compatibilism, consequentialism, contextualism, correspondence theory of truth, deontology, egalitarianism, empiricism, Humeanism, libertarianism, mental content externalism, moral realism, moral motivation internalism and externalism, naturalism, nominalism, Newcomb's problem, physicalism, Platonism, rationalism, relativism, scientific realism, trolley problem, theism, virtue ethics
Note
Thanks pragmatist, for attaching short (mostly accurate) descriptions of the philosophical positions under the poll comments.
Post Script
The polls stopped rendering correctly after the migration to LW 2.0, but the raw data can be found in this repo.