Conversely, do you not function test a firearm after putting it back together?
There should be NO AMMUNITION at your cleaning/dry-firing location. One of the more common negligent discharges occurs AFTER cleaning and reassembling, doing a function check, then loading it while still seated at the cleaning desk, and doing another function check because that's what you do at the cleaning desk. Oops.
UNLOAD, leave ammunition in another room, take Glock (or any gun) to cleaning area. Verify unloaded, and disassemble, whether it requires pulling the trigger or not is not an issue anymore, and you'd better be doing the same verification whether it is a Glock or not.
I don't even know you and I already know there is no way on the planet you can be even close to being as arrogant and stupid as that DEA agent.
I think Taurus is the one that likes to advertise how you don't have to pull the trigger to clean their Glock-like guns. Taurus is also the same marketing department that brings you the most powerful handgun in the world, firing a .410 shotshell, even though they didn't invent it, because it was a failure 15 years ago. Taurus is also the same company that touts their double-strike feature on their Glock-like guns. Sure, their heavier/longer trigger pull gives you a second chance at firing bad ammo. When was the last time you had factory fresh centerfire ammo not go off? And are you seriously supposed to aim at the bad guy again and hope it goes off a second time anyway? If this was really an issue, we'd all carry revolvers and bring a fresh round into play at the same time. Taurus has the finest marketing department in the firearms business.