"But It's Our Minhag/ Mesorah!"
I didn't think that there was anything more to add to the Kezayis topic, but it always grows!
As you know, the arguments for a kezayis being a kezayis are overwhelming. But I've heard an interesting counterargument from some people. They do not even attempt to counter all the proofs from the Gemara, from the Rishonim, from the Acharonim. They simply say that any such proofs are irrelevant; the fact is that our minhag/ mesorah is to use a much larger shiur.
Now, I certainly accept that tradition can be a trump card (in fact, that's one reason why I personally don't wear techelet). But here's the thing: it's not a tradition, according to any reasonable definition of the term.
I am absolutely certain that for at least the vast majority of people, if not everyone, their great-grandparents and even their grandparents were not brought up to measure huge shiurim of matza. In fact, for many people zealously espousing the larger shiurim, probably even their parents don't. It's not a family tradition, and it's not even a community tradition. And as R. Hadar Margolin has documented, even renowned rabbinic authorities weren't doing it. It arose a couple of decades ago, in line with Haym Soloveitchik's seminal article "Rupture and Reconstruction" about "book-tradition" replacing actual tradition.
So when someone says that their minhag or mesorah is to use a larger shiur, in many cases what they actually mean is that identifying with a particular contemporary culture is more important to them than classical halachah or actual tradition. This is not necessarily an illegitimate argument; but one should acknowledge what is really being said.