You are absolutely wrong.
There is literally no difference if the option wins. If it doesn't, the option would be contributing different things to the vote tally.
Palace via only one Secondary is not going to exist because we cannot take less than Main; so it's an action wasted in a weird case of not winning both actions.
Same goes for Integration.
So I have no idea what do you want to achieve by such a switch.
With an unstated:
C) Significant loss of Stability will undermine our argument that our culture is more stable and happier by making people unhappy and the system unstable.
That's a speculation easily countermanded by us being able to so many people in due to stable enviroment.
A) It increases the impact of our prestige upon the people.
Not only; it also means that we not only talk the talk about acceptance, but also walk the walk. If we take the least option, they may well go "Eh, that's not much to take; you are not really willing to sacrifice shit for your ideals of acceptance, you are just talking a big talk". Putting money (or, rather, Stability) where our mouth is is a good move all on its own.
Besides, taking in refugees never ever raised our Prestige by a single point (if you can quote an update which says we actually
do gain Prestige for it, feel free to quote it - it would be an evidence to back your otherwise so far unproven position), so I have no idea where this whole thing about it being Prestige-related is coming from.
Taking in refugees has a chance of being a boon in debate most likely either because of proving that our environment is that stable or because it means we are willing to live up to our ideals instead of abandoning them in the face of even the sllightest discomfort or trouble.
"Not living up fully to our ideals becuase it is a bit hard" is an apt description of taking -.5 instead of -1.5 when in situation with no chance of dying due to it, by the way. Or at least it can (and will, I imagine) be viewed this way in debate if it ever comes up...granted, debates are mostly about Spiritual values, so it is unlikely, but still.
And yet the lowland cultures have more values in common with each other than with us, because we're isolationist.
A big part of the Stability hit is that the refugees all bring their own cultures and way of life with them, which we expend Stability to mesh their practices into ours.
Cosmopolitan Acceptance is not just about accepting people from other cultures. The difference between Cosmopolitan Acceptance and Land of Opportunity is that Cosmopolitan Acceptance believes that foreign cultures have value(which is reinforced by accepting foreign cultures), while Land of Opportunity believes that we should help people(which is reinforced by refugees).
I do not imagine Thunder Speakers culture has
anything in common with Swamp People culture, for example. As opposed to them, due to some time being neighbours, prrobably having at least something in common with us. Honourable Death or whatnot.
Highlanders have us-inspired Law and us-inspired farming, so at least two of their social values are most likely modified versions of Justice and Stewards of the Land or something in such vein. Again, most likely more in common with us than with Swampers or Thunder Horses.
We have no idea at all about values of other two beyond them living in wildly different environments with wildly different origins and approaches to warfare and farming. That...does not suggest huge similarity.
So, again, you taking "lowland cultures have more values in common with each other than with us" and using it as a basis of argument instead of thinking about it undermines your whole argument because it is most likely false, almost guaranteed so for at least Highlanders.