Its more of a problem in Israel where its really hard to buy stuff without buying Kitnyot.
I think a better example would be if you moved to a new community you were supposed to take the minhagim of that communmity (Prior to WW 1 when people did not move as much) So an Ashkenz who moved to a sephardic country would become a Sephard and Vice Versa. Today Sephardim and Askhenzim are intermixed and its harder.
Quinoa is a better example of Kitniyot going wild. Exactly why some think its kitnyot makes people question the entire minhag. Quinoa is a berry not a legume. It is closer to a blueberry than a pea yet some have delcared it Kitnyot.