You left out a pretty important detail. Your "insurgents" in America aren't shooting people or planting IEDs. Communicating and protesting, on the other hand, are sacrosanct rights in the US.

You're missing the forest for the trees here. The network and techniques used here are the same, but even more refined and tech enabled, of those insurgency groups. The power is the network of people in their specialized roles that can quickly target the enemy (ICE) and deliver a payload (obstruction).

The FBI has a long history of attempting to infiltrate and destabilize these groups. In the early 2010s there was a push to infiltrate right leaning groups. They especially called out in their published documents disgruntled veterans returning from the wars and unhappy with leadership noting a worry they would use the skills picked up at war at home.

It's absolutely no surprise that the FBI would investigate this behavior.