Personally, I think based on the responses here, forgive me if I’m wrong, everyone seems to operate under the Umineko assumptions, i.e. Each ‘world’ Rika enters plays out the events before and after the fifth Watanagashi festival has a different ending. However, it’s never mentioned that that is the case.
While in Umineko, it was understandable that each arc HAD to be different, since Yasu was writing a fantastic mystery (or a mysterious fantasy, whichever is you cup of tea, no puns intended), she couldn’t possibly write a same set of events in each iteration of the Rokkenjima Massacre. However, if you were to put it in the Higurashi perspective, it’s not impossible at all for the same events to repeat. If we now put it in that perspective, it means it’s possible Rika has already gone through a world where she unwittingly let Akasaka go about with his snooping, and later suffer consequences we all can imagine. It’s also possible that Rika might have let him meet the same end after hearing about his wife’s untimely death, hence her severing of the phone lines.
Furthermore, we may extrapolate that Rika revealing her knowledge of the events to come might also have been part of a means by which she tries to convince Akasaka that she knows every future to come as well, with her cutting the phone lines and seeing through Akasaka’s apparent reason for staying in Hinamizawa. It’s possible that she first opens up to Akasaka alone because she can be sure Akasaka won’t fall prey to the Hinamizawa syndrome and is thus not susceptible to completely irrational conclusions. While she can’t convey the same to Ooishi because she knows his first idea will ne to dismiss her for the psych ward, or to any of her friends, all of them falling prey to the Hinamizawa syndrome (of course this later is refuted, but at present she still can’t convey the same due to her seemingly endless wait for a miracle), or even to Irie, Takano or Tomitake, all of whom die before the incident can take place, and all directly or indirectly responsible for her parents’ deaths.
Personally, I feel Akasaka is an Author’s Device for conveying what we as readers would have done in Hinamizawa should we have been trying to solve the mystery, subject to more than a few character constraints, of course. And of course, this may apply to all first-person perspectives in Higurashi. I suppose that’s the beauty of the first-person perspective, where the characters in a touching story such as this can actually resonate with the readers. On the other hand, Umineko may have done the same with Ange, but I won’t say more on the matter since it’s not exactly relevant.