While there is no question that the First Amendment protects coverage of spot-news events in public places, it is also clear that private events may be legally controlled by their organizers. Organizers may say who may or may not attend. They may also require that attendees agree to certain conditions.
Journalists are equally free to decline to agree and simply stay away.
Good advice to photographers – beware what you agree you can('t) do with your images when shooting an event. The obvious problem for journalists is that standing on higher moral ground isn't really an option. If you don't shoot an event, someone else will, and they'll have the published photos to prove it.