Lord Haseo said:
It's not really a bad idea to begin with. If Luke were to tell Kylo Ren about the dangers of the Darkside you people would have no problem with it. But because one strand from the prequels would be in the ST then suddenly the idea is shit. Let me ask...who would know most about how toxic the Darkside is? Anakin of course seeing as how he was engulfed in it for decades. I don't see any reasoning for that being a bad idea other than "its bad because prequels"
Obi-Wan's ghost, apart from being an exposition delivery vehicle, was there to provide some bare minimum of guidance for Luke on his path to becoming a Jedi. Luke's final glance at the ghosts of his three "fathers" at the end of ROTJ is only meaningful if it is just that - a final glance - which the film strongly implies it is by showing Luke finally turning his back to them and rejoining the world of the living.
Luke emerged from the OT as a fully-formed Jedi. Having the Force Ghosts linger on into the ST would not only diminish his role as the elder mentor figure for the new characters, it would also diminish the very concept of death (at least for Jedi) in the saga. What meaning does Obi-Wan's sacrificial death have (or Anakin's for that matter) if they can just continue to appear in the films and interact with living characters, differing from their former living selves only in that they are a bit bluer and more translucent?
Anakin's story - his arc - is finished, I'd have thought that that was one thing PT haters and lovers could agree on. It falls to Luke to impart wisdom and warnings to the youngsters now - and, as hero of the OT (and the PT too if you consider that he is his father's redeemer), nobody has earned that duty more than him. To have him sit passively off to the side while the ghost of his young-looking father lectures the new villain about the evils of villainy would be all manner of lameness and shite, and we can only be grateful that it is so exceedingly unlikely to occur under the watchful eye of the ST's creative team.