I don't have time to read this entire thread, but from the apparent butthurt leveled at Riker as evidenced by the first dozen or so posts here, some of you should take this into consideration.
Just as Riker's behavior at first is dickish (because of Ro's actions leading to the death of eight other officers), it's also literally his job to enforce ship rules. It's against the fucking rules to wear any non-standard apparel or ornamentation. So in Riker's eyes - whether it's religious or not - she shouldn't be wearing the earring on duty.
Why then does Worf get to wear his baldric? Because he's earned the special dispensation to do so. Literally no evidence is given about why Worf wears the thing throughout either this series, the four films he appears in, or his four years on DS9. So we can assume that it's presence could be due to any number of reasons, but the most likely - based especially on Riker's reaction here - is that its a special dispensation kind of thing, that Picard allows because he knows Worf is a solid officer.
When Ro arrives on board, she has done nothing yet to prove herself as same. And by the end of the episode, she's done exactly that - proven herself (to Picard and Guinan, anyway) and that's why Picard okays the earring.
Lastly, none of us knew, when "Ensign Ro" aired in 1990, how integral and important the Bajoran religious faith was. That element of their culture was not established until well after the episode had aired during development of DS9. So, it's a little silly to get so up in arms over such a minor instance like this.