Isn't this like saying every historian must believe in time travel? Just because you can't visit someone doesn't mean you can't learn from them.
Who is it that's speculating about quantum communication? Certainly not physicists. It's mostly just IFLScience!-class journalists seeing a term like "quantum teleportation" and assuming that it means start trek is real and write their articles based on that.
> I believe that everyone at SETI must believe FTL is possible because otherwise it truly is a waste of resources.
If everyone at SETI believes that mysterious FTL communication exists, then why do they spend all their time looking for EM signals?
If we detect radio signals in another galaxy but FTL is impossible who cares? The human species will be extinct before any interaction can occur. It's probable that whatever species sent them is already extinct because it's at least 3 billion years old.
If c is the ultimate speed limit there's really no point in looking anywhere else because everything else is so far away it's irrelevant.
We get generation ships, and if we are extremely lucky, we may have some very patient pen-pals, but warp drives, ansibles, and their attendant paradoxes are pretty unlikely to be features of this universe. Personally I prefer a knowable universe to a tourable one.
If FTL isn't possible then the end result of listening is simply the confirmation that something else exists and it stops right there.
Don't you think there's at least a little bit that could be learned by listening to alien communications from centuries ago, other than the fact that it exists?
If such signals were found, would you really stop reading at the headline "alien communication discovered"?
Why is that? Special relativity already demonstrates that space contraction at near light speed would allow interstellar travel at human scale duration, with the side effect of time dilation for moving observers.
Probably true on a species level, but you are vastly underestimating how long a planetary-level timescale is. A von Neumann probe could cover the entire Milky Way in relatively short geological time.
We've had radio for just a little over 200 years and we've already realized its limitations. The fact that we can even speculate about quantum communication leads me to believe that radio is definitely NOT the end-all-be-all. If you scale human civilization into a 1 year time frame we invent radio at 3PM on December 31st. It's successor likely emerges January 2nd at the latest. Radio communication is likely a blip.
Radio is efficient over short terrestrial distance but horrible for long (galaxy scale) distance communication. If interstellar travel is feasible at all it will have to be at FTL speeds and an FTL communication system would be necessary.
If FTL is truly impossible then it doesn't seem like there is much point in listening since everything is so incredibly far it's irrelevant even on a species-level or planetary-level time scale. I believe that everyone at SETI must believe FTL is possible because otherwise it truly is a waste of resources.