I don't know if they oppose ALL defense spending. But sometimes I think they are advocates of a Soviet-style "Quantity over Quality" force structure. The US public will never accept huge losses, so they are advocating something that will never happen. I think that they keep pushing the rock in that direction, however.
The CDI is full of former officers who think their military gravitas allows them to promote appeasement policies. It's a kind of political 'bait and switch' tactic, Alinsky-like dissimulation. I have no doubt that most of the officers are sincere, but that just means they fall into the 'useful idiot' category.