Oro cant just Kill Naruto cause Jiraya and Tsunade is protecting him and those two are at least as strong as Oro or even stronger.
Also Naruto is getting stronger all the time so if Oro wants to kill Naruto he should try to kill him now before he gets to strong to be killed by Oro.

When Oro finds out what Naruto does to Kimimaro (if Naruto kicks kimis ass) then Oro will probaly be after Naruto.