I had a couple different thoughts on this and had some theories after reviewing the episode again.
There are a few things that point to a potential answer:
- When approached by a fan David says that "The human experience, the survival of the human body, of life, is central to the mission". This would indicate that part of their mission is to understand how to maintain the human body in an unconscious state while transmitting the consciousness, and to help understand how the human body would react in space over the long term.
- The weekly physical is another example that could show they're researching how the human body would respond to being in space for such an extended time.
- Cliff says to his wife at one point "It's a two-man ship, it relies on both of us". I would imagine that they would find it more likely that there would be an issue with the link rather than with the human. So if the links were up there and the connection got severed the ship would be useless, and we know the US government would not want to leave their precious technology floating idly through space. For example, if the cult had come to David's house and killed his human body or if they died for any other reason, then the entire mission would have been kaput. Even with the catastrophes that occurred in the episode the mission can continue, which I'm sure is the main concern of the government.