Because just as a Torah scroll is invalid if even a single letter is missing, so too the Jewish people are handicapped if even one Jew has fallen away from our people.
Every Jew is crucial, an indivisible part of the whole.
Before Purim, the rabbi put out a plate and told everyone to give a half-shekel (or its local equivalent).
I understand this was done in the times of the Tempe to purchase public offerings. When the Torah instructs every Jew to donate one Half-Shekel annually, the law is that everyone must give exactly the same amount.
Volumes have been written about what is proper speech and about what constitutes an abuse of this unique capacity to verbalize with which man was endowed.