I have my own terutz for eating kitniyot. But, the pro-eating argument in the decision is still significantly connected to the concept of projecting a message, "to show that you're from Israel." It sounds antiquated, or unpopular, but there is no halachic task upon us to "show" that we are from a certain locale.
The only "show" task we have is to dress differently so as to look differently from gentiles. Maybe another task is to look decent, and not ostentatious. I can't think of other tasks like that.
But the rationale of appearing as someone from Israel, besides reminding me of Machon Meir mentality, reminds me of Reform synagogue, unfortunately. I remember when my dad and I drove around on Shabbos looking for a shul, the only one we found easily was a huge building of a reform shul. Therewe saw a lot of strange things. So when my dad and I asked the people why the tallis were small, why they prayed like Christians, why they prayed in English ("you're Jewish, right?"), why the women sat with men, why the American flag, why A, B, C, they answered that to know, to show that this is modern times, we are in USA and the religion must reflect the surroundings.
So the answer to the Kitniyot decision is that they are too sure that kitniyot-eating is specific to Israel. Most of Israeli population now, unfortunately, is eating a mixture of chametz with token matza. Religious Sephardim are eating kitniyot. But the Machon Meir thought gets caught up in assumption that Sephardim are the Israeli-specific thing.
The way we can examine Yemenite and Ashkenazi culture, we can also strongly suggest that Ashkenazim and Teymanim are probably from the same region of Israel, prior to the Destruction of the Temple, and why should we Ashkenazim suddenly mix our identities? Protecting the minhagim of the family, clan, and place of roginin is a very serious concept in Halachah. When discussing the Teymanim people usually go gaga and say "how cute" the Teymani minhagim are. Nobody suggest that they change their minhagim. So by the same token, why should Ashkenazim? At Machonn Meir they didn't see the conenction of this logic, " mah kesher?"
Another strong reason for abstaining from kitniyot is the way it is written is Shulchan Aruch, sif 453. Rama reminds that many authorities tried to literally cancel the minhag, but "nichshalu", as I understand, they "ran into problems," if not "failed," andrealized that the authority of the rabbis that insituted the abstention has been ever so wise.
My own terutz, which is also connected to appearance, to eat kitniyot, is that many arrogant shkenazim offhandedly say that because Sephardim eat kitniyot, "they eat chametz. " Since we are concerned with "maaris ayin," and we don't go into McDonald's to drink a cup of water, we don't eat fish blood (though it's permitted) -- so that a Jew, arrogant, judgmental, uninformed, or whatever - will not come to a wrong conclusion.
I think we should eat kitniyot to erase the possibility of creating such a false impression about a group of Jews. As long as the kitniyot have a Badatz rating, which they can easily have.
I have seen though, sunflower seeds, corn, shelled peanuts, being leniently and arbitrarily consumed, wherein I personally thought of these foods having been kept from before Pesach by the person.
I spoke to a guy from a kibbutz up north and he said that corn, sunflower seeds, and things that grow above ground are harvested by the same combine that harvests wheat. They just change the front attachment. He strongly believes in abstaining from kitniyot. He reminded me that as far as canola, which is grown in Canada and US, since on fields it is often rotated with wheat and rye, for purposes of enriching the soil as well, it is enough for one stalk of stray wheat to render an acre of canola crop unfit for Pesach.