Williams doesn't say who the arsonists are but it's pretty clear he's talking about Trump and Trumpists:
WILLIAMS: After 28 years of peacock logos on much of what I own, it is my choice now to jump without a net into the great unknown, as I do for the first time in my 62 years.
My biggest worry is for my country. The truth is, I'm not a liberal or a conservative. I'm an institutionalist. I believe in this place and in my love of my country I yield to no one. But the darkness on the edge of town has spread to the main roads and highways and neighborhoods. It’s now at the local bar and the bowling alley, at the school board and the grocery store, and it must be acknowledged and answered for.
Grown men and women who swore an oath to our constitution, elected by their constituents, possessing the kinds of college degrees I could only dream, of have decided to join the mob and become something they are not, while hoping we somehow forget who they were. They've decided to burn it all down with us inside. That should scare you to no end as much as it scares an aging volunteer fireman.
[I]t has been and remains a wonderful life. It's as if I'm gonna wake up tomorrow morning in Bedford Falls. The reality is, though, I will wake up tomorrow in the America of the year 2021, a nation unrecognizable to those who came before us and fought to protect it, which is what you must do now.