I could be wrong, but I think @CellBlock1138 means Han being a ghost (which Han is not) is what he thinks is dumb. And if that was the case, I would agree 100%. At least that's how I perceived it. I also think it's mentioned in the film that Han is there as a memory of Ben's, or something close to that.Again, NOT HAN'S GHOST!
A representation of Han, in his mind, that he's talking to. Which people who have suffered loss actually have experience with in real life. Like me. So, by proxy, saying that Ben "talking" to Han is dumb, is the same as calling me dumb for asking my "mom's" advice.