It’s not all or nothing here. We spend too much and get too little out of it.
Currency counterfeiting is a different set of laws than interstate financial fraud, which is a different set of laws than throwing a Snickers wrapper on the ground in Yosemite.
Which is somewhat irrevant. Teams dealing with each can still share headquarters, IT resources, support stuff, cafeterias, and lots of other things.
As for IT functions, all of that should be centralized under the GSA with proper security controls. There's no benefit to having every agency maintain its own IT infrastructure. Most of those staff are redundant and could be laid off.
This argument doesn't hold.
This works for email. Would you work at a company where you had to build and deploy apps on infrastructure controlled by someone in a different department and location, whose boss gave them the mandate to standardize as much as possible to reduce costs? (Hope you like Oracle…)