That's not really true Ellie, people can have similar dreams about flying, yet their experience of those dreams can be different. One can find it liberating, another can find it frightening. Sometimes the same person can be frightened in one, exhilarated in another and meh about it in others
Except that there's one thing that's common to all of those dreams - the dreamer is not really flying. Dreams are distinct from reality - this we know. We make that distinction all the time, but we abandon it entirely if we decide that we'd like to believe that it's saying something we want to hear - "My mother is visiting me", for example. This is not rational.
Surely it's not about whether people are comforted or not, you are missing Pedro's point, I think. It's whether it's true that dead people visit people via their dreams. That people feel comforted is nice, but neither here nor there in a discussion about whether or not it's true.
It is analogous with the idea that religion gives people hope. Well, OK. Doesn't make it true, though. What's true for one person is true for us all, if the word "true" has any meaning.
The difference is that my reasons for rejecting the idea that my mum visits me occasionally in my sleep is because I've taken ALL the available evidence into account. If I were to believe that she was, it could only be because I'd ignored that evidence. So the two positions are not equal.