[...]We need express no opinion as to whether the State in some circumstances might limit the exercise of the franchise to those "primarily interested" or "primarily affected." Of course, we therefore do not reach the issue of whether these particular elections are of the type in which the franchise may be so limited. For, assuming, arguendo, that New York legitimately might limit the franchise in these school district elections to those "primarily interested in school affairs," close scrutiny of the § 2012 classifications demonstrates that they do not accomplish this purpose with sufficient precision to justify denying appellant the franchise[...]