Regarding the referendum thing, and the comment that someone made about using referendums for everything, that would be insane. No democracy holds referendums for every little thing that happens. That's why we have rules instead, so that those who are voted into positions of leadership don't have to continually bug their "constituents" on every little topic. The fact that we, in this forum, actually have a say on every single rule is a huge step in a positive direction, compared to any country's democracy you'll find on the face of this planet.
Back to the topic of the word delusional, perhaps a different, more precise, term should be used, such as "incoherent". For instance, "People may not engage in behaviors that are both persistently disruptive and blatantly incoherent." As we're not putting people's personal views and beliefs on trial, but the rule is trying their ability to present themselves in a social setting, I think a word that applies to the aspect of communication between people is more proper than a word that relates to a person's internal struggle at relating to the external world.
This change would NOT cause problems with people who merely don't speak/write English very well, as the criteria for communications being disruptive would still need to apply but they wouldn't apply if the only "problem" is in the poster's ability to string together sentences according to formal English rules.
This vote is only two days away from ending, and if it gets passed as is but still people dislike the term "delusional", then we could start an "official" discussion thread on the matter. Then if we come to some sort of consensus through discussion about a better wording for the rule, then we can always start up a new vote as a request to change the one word of the rule that seems to be drawing all of the contention.