The CIA operates in stealth; it is associated with some of the worst abuses of power in recent American history, including assassinations, coups, and torture; it has military capabilities. Congress needs to be firmly in control of its relationship with such an agency. The Constitution demands no less.
The ABA’s report said that if a President thinks a law contains unconstitutional language, he shouldn’t sign it. To me, that is Ivory Tower impracticality. Take the 2011 Appropriations Act; if Obama hadn’t signed it, the government would have shut down. Would it have been remotely responsible for Obama to have done that? Such purity would make government impossible. Signing statements are actually a good alternative to such chaos. The President asserts non-aquiescence, government moves on, and the courts can sort the matter out if they need to.