Why do the trill need a symbiont if the Guardians can transfer memories?

Question

DS9 "Facets":

DAX: The zhian'tara is a ritual where joined Trills get a chance to actually meet their previous hosts.

KIRA: Meet them? How?

DAX: That's where you come in. If you don't mind, I'd like to borrow your bodies for a few hours.

O'BRIEN: What do you mean borrow our bodies?

DAX: If you agree to participate, the memories of one of my previous hosts will be temporarily removed from the symbiont and imprinted onto you. You essentially become one of my hosts for the duration of the ritual.

BASHIR: And how is this accomplished?

DAX: The memories are transferred telepathically by a Guardian.

After multiple hosts are inserted and removed telepathically by the guardian, this dialogue happens.

CURZON: In that case, you'll be happy to know that I've come to a decision that's going to benefit both of us.

DAX: What do you mean?

CURZON: I've decided to stay where I am, in this body. And I'm not just speaking as Curzon. This is Odo's decision as well. We like what we've become and neither of us wants to go back to the way things were.

[Commander's office]

GUARDIAN: There's no way to remove Curzon's memories from Odo without his cooperation. He has to give them up willingly.

SISKO: What'll happen to Jadzia if we can't persuade him?

GUARDIAN: It'll take some time for her to adjust to the new balance, but she'll be fine.

SISKO: Do you want me to talk to Curzon? I know him better than anyone. I might be able to get him to cooperate.

DAX: I don't think so. I don't think I want to do anything.

SISKO: What do you mean?

DAX: I mean I'm fine, and obviously Odo and Curzon are well suited to each other. Maybe it's better this way.

So we see that the guardians can transfer memories from hosts to hosts and that process can be temporary or permanent without difficulty. It's difficult to remove a trill from a host and place it in another.

Why not just take the memories out of the host, or out of the trill and place them into a new body as needed? Why bother with all of these symbionts? In the least they could share lots of hosts with more people. For example Jadzia could get a symbiont but the could take the memories of a couple of her hosts and transfer it to others of her species so more could partake at least in some part of the joining process.

Answer 1

The series bible for Star Trek: Deep Space Nine says that

Many centuries ago, the symbionts lived underground, while the humanoids were on the surface ... and due to an environmental disaster, they were forced to 'join' to survive.

However, what exactly happened, is unknown. Something did, and most likely shaped the tradition of Joining Trills and symbionts.

Another point is that a person who joined with the memories of a single host, instead of the symbiont itself, has to "switch" personalities. They're either themselves or the other guy. It's like a spirit possessing a living being...usually not a nice thing to happen to the latter. You can see that in the scene where Quark constantly interrupts Jadzia's and one of the previous Dax's conversations. They can't be one at the same time, there's no new personality, no new existence created, it's just two separate individualities in one body, fighting (or not) over control of it. The unexpected exception is Odo, the Changeling*.

It's also unknown if you can imprint the memories of more than one host. It's almost like building a multilayered schizophrenia.

The tradition of Joining is there because the Trill and symbiont become more than a sum of individual parts, and not a many-faced Bad Cop/Good Cop from the LEGO movie.

• here's the part where they talk about that. Odo/Curzon goes to visit Captain Sisko. I'm pasting most of the conversation to give it some context.

  SISKO: Curzon?
  CURZON: Don't tell me. The nose gave me away. What's the matter? Aren't you happy to see me?
  SISKO: Of course, of course. So where's Jadzia?
  CURZON: It's all right. I told her I wanted to come see you, that we'd meet up later at Quark's. I'm going to give that little toad the scare of his life.
  SISKO: You sound like Odo.
  CURZON: I am Odo.
  SISKO: I don't understand. I thought you were Curzon.
  CURZON: I'm both. The Guardian thinks it has something to do with my shape-shifting nature. It's as if Odo and Curzon have been joined. It's proving to be quite interesting experience for both of us.