Echo chambers are the dread of good defence policy and military theory progress. People in an echo chamber don't respect and probably don't even get to hear or read conflicting views or evidence, instead all of their intake is from people with similar opinions.
Echo chamber groups avoid the mean cognitive dissonance, but the price is intellectual stagnation and the inability to overcome incorrect or outdated paradigms. Such echo chamber groups rapidly agree on a favoured narrative, and then proceed to laud each other's reciting of kool aid as "thoughtful" or "strategic thinking".
This may sound like the complaint of someone not allowed to join a particular echo chamber group, but I'm really, really glad that (as far as I know) I never joined any such group. Some people appear to be more well-suited for such memberships than others.
The problem with this groups in regard to mil theory advances is obvious; almost all of their output is mere noise of no value, similar to most obligatory master's theses.
The problems caused in regard to defence policy (or "security", military policy) are probably not as obvious: Such echo chambers tend to be stiff and incapable of adapting to changing circumstances sensibly. Changing circumstances are rather exploited as an excuse to bring forward the same old wish lists - or even longer ones. This is somewhat similar to how inflation hysterics keep demanding higher central bank interest rates because hyperinflation is just around the corner ... for decades.
Many politicians in the office of minister of defence (or equivalent) are no experts on defence. They're rather experts in politics, in fostering networks and a political base, and may have had prior experience in heading some bureaucracy (executive office). They may then come under influence of a whole array of echo chambers, some of which were propped up by the arms industry because their reliably monotone message suits their interests. Most echo chambers will readily provide a message the minister of defence wants to hear: "Defence" deserves more prestige and a bigger budget and the MoD should engage in high level foreign policy.
It would be very, very valuable if the politicians recognize the echo chambers as what they are, not as pools of defence thinking excellence. Right now I couldn't name a single minister of defence who ever beyond doubt did so.
Another dream is about a world in which echo chambers were cracked open, and discourse is effective at finding fine answers to important questions. This dream appears to be very outlandish, though.
P.S.: There are echo chambers contra big spending as well: POGO, the "Military reform" gang, "fighter mafia" and most if not all of the usually completely ineffective pacifist groups qualify (or qualified) as echo chambers as well..