Suppose there were an organization for kids that accepted kids of every religion except for Jews. Maybe they explained that they promoted religious unity and that the Jewish idea that they are God’s chosen people doesn’t square with the organization’s message. Suppose they came to your local public schools and wanted to recruit students (gentile students) for their organization. What would the reactions of parents and teachers be? My guess is that even nonjews would find it distasteful for public schools to promote an antisemitic organization.
Or suppose that the organization accepted kids of every religion except Catholics. Now what would the reaction be? My guess is that it wouldn’t be enthusiastic. Even accepting kids of every religion except Islam would be frowned on.
All around the country, Boy Scouts routinely recruit new members at public schools. They welcome kids of all religions except atheists.
PS: This analysis isn't anything that hasn't been said before.