So how do you rationally decide if an action is right or wrong? -- or are you saying you can't do this?

There is no such thing as "rationally deciding if an action is right or wrong". This has nothing to do with particularism. It's just a metaethical position. I don't know what can be rational or irrational about morality.

Again though, I'm not a particularist, I do have principles I can apply if I don't have strong intuitions. A particularist only has her intuitions.

Also, just to be clear: you are saying that you do not believe rightness or wrongness of an action ultimately derives from whether or not it does harm? ("Harm" being the more common term; I tried to refine it a bit as "personally-defined suffering", but I think you're disagreeing with the larger idea -- not my refinement of it.)

I don't believe my own morality can be reduced to language about harm. I'm not sure what "ultimately derives" means but I suspect my answer is no. My morality happens to have a lot to do with harm (again, I'm a Haidtian liberal). But I don't think that makes my morality more rational than a morality that is less about harm. There is no such thing a "rational" or "irrational" morality only moralities I find silly or abhorrent.

I tried to make it quite clear that I do care about the rest of the world; the fact that I don't yet have a solution for them (and am therefore not offering one) does not negate this.

If it's the case that you care about the rest of the world then I don't think you realize how non-ideal your prescriptions are. You're basically advocating for redistributing wealth from part of the global upper class to part of the global middle class and ignoring those experiencing the most pain and the most injustice.

I also tried to make it quite clear that my solution for Americans must not come at the price of harming others in the world, and that (further) I believe that as long as it avoids this, it may be of some benefit to the rest of the world as we will not be allowing unused resources to languish in the hands of the very richest people (who really don't need them) -- leaving the philanthropists among us free to focus on poverty worldwide rather than domestically.

But of course it comes at the price of harming the rest of the world. You're advocating sacrificing political resources to pass legislation. Those resources are to some extent limited which means you're decreasing the chances of or at least delaying changes in policy which would actually benefit the poorest. Moreover, social entitlements are notoriously impossible to overturn which means you're putting all this capital in a place we can't take it from to give to the people who really need it. Shoot, at least the mega-rich are sometimes using their money to invest in developing countries.

This doesn't even get us into preventing existential risk. When ever you have a utility-like morality using resources inefficiently is about as bad as actively doing harm.

You seem to be arguing, however, that actions can be wrong without causing any demonstrable harm. Can you give an example?

None you'll agree with! You've already said your morality is about preventing harm! But like it or not there are people who really don't care about suffering outside their own country. There are people who thing gay marriage is wrong no matter what effects it has on society (just as there are those, like me, who think it should be legal even if it damages society). There are those who do not believe we should criticize our leader under certain circumstances. There are those who believe our elders deserve respect above and beyond what they deserve as humans. There are those who believe sex outside of marriage is wrong. There are those who believe eating cow is immoral; there are others who believe eating cow is delicious. None of these people are necessarily rational or irrational.

I'll reiterate one question: What do you mean by rational in "rational morality"?