They don't need to round up 100 million.
Heck, after a couple hundred of the most outspoken get carted off, neighbors will be ratting out neighbors to save their own butts.
This has been done before, there are instruction manuals.
If you don't feel comfortable killing the agents' wives and little children while their Daddy is off at work, you've already lost.
“Do you really think they’re that stupid?”
Yes, I actually think they’re that stupid. If you paid attention to the ATF attack at Waco, any grunt PFC can figure out how to kill them all. And if you did any reading on cop sites, you would know that the first order of business is to head home and protect their families if TSHF. That was proven during the Los Angeles riots in 1991, and proven again when the NYC fat-ass cops stood by after Sandy and let the looters take whatever they wanted.
Killing the innocent is never an option. That is murder, pure and simple. Killing the agents is preemptive self defense. If you know where to find the families, you know where to find them. Snipers, IEDs, car bombs, planned home invasions resulting in only one "victim"...