Well first, I think I was not clear enough since there seems to be a whole misunderstanding on the matter.
1) I was not refering to Kresh, or Kresh tea, which is more or less canon. Also, Kresh tea is lethal to Caldari people too, even if they may be more resilient to it since it is from their homeworld, which makes a decent amount of sense. Imply genemodding or whatever, I don't care. I could care, however, that involving genemodding would be the exact same thing : making up something that is not specified in the wiki. 2 dangers : steping on someone else's RP, and more importantly, risking to see the PF someday explain it, but in another way.
2) I am not complaing that my character can't do it so that's unfair or I don't know what. I couldnt care less what my character can or can't do. She has her pros and cons, and considering her catastrophic constitution even a decent dose of alcohol could kill her, something I have already played from times to times. It's not about my character.
3) No need to play on hyperboles. I have no problems at all with evolution and patterns or explanations leading to resilience, or whatever. Hell, we already have the Caldari being the technologically advanced people of the cluster, and that is canon. I have no issue with that. That's part of their flavor, like Alpha cities are part of Gallente, or that half the cluster belongs to the Amarr bloc. I am not even sure why this comes into question here.
4) The Caldari are extremely cliquey. Yes they are, it's more or less canon and it reminds a little of the japanese culture as well. We all know that some bits of Caldari remind the japanese extremely insular culture that even today sees strangers as mere "gaijin", like some bits of Amarr remind that culture as well on different points. Or like the Amarr borrow a lot of persian terminology, or the Minmatar a lot of Norse mythology, etc. That is, also, part of their flavor and I approve the cliquey bit.
5) Character bios can be disregarded by some people if some things are not based on the Canon or doing the exact same thing for me. A character bio is just a form, like any RP. It can contain perfectly common stuff, borderline stuff like that or napanii, or stuff conflicting with the Canon. I am not saying that everyone should systematically disregard what is not specifically written in the Canon, but merely stating that something that is not Canon is exposed to more or less debate depending on its sensitivity. The same way that the more you claim to have a RP impacting on other players' RP, the more there is a risk that these concerned players can react negatively to that.
6) Kresh is not totally similar to gluten from what I understand. It would be like saying that some people are immune to diffuse arsenic or whatever. Of course, as everyone seems to agree it's merely about resistance here, and not immunity... The point is moot.
Edit : to make it even clearer, I already took an issue with a few Caldari players in the past for similar reasons, even if they were less "minor". It was OOCly about whether all Caldari or just a part supported the retaking of Caldari Prime, which was (at least at the time if i'm not mistaken), not stated in PF. It was thus conflicting with my very own understanding of PF and since it was an OOC issue, it was even barring us to settle it ICly in the first place. That's my issue.
For the rest, I find the actual discussions about Kresh interesting.