If someone in the US posted publicly about bringing "bottles, fabric, gasoline, turpentine, foam plastic" to a protest, they'd get a visit from the FBI. Speech that incites violence is something they investigate regularly.
The first person of interest would most likely be the user of the IP address at that time.
It's unfortunate that operators of Tor exit nodes have a large amount of risk placed on them, but I don't think it's a situation borne of Soviet-era backwardness or unique to modern Russia.