Secret services discretly attending demonstrations is common practice.
Every country in the world does that, even in ultra-democratic countries in Scandinavia.
In Russia everyone is spying on every one now, citizens are pushed to snitch on each other by the FSB. Any Russian citizen complaining about Russia’s war on Ukraine, gets a 5 to 15 years of prison at best, or Gulag-time at worst.
Simply uttering the word “war” in Russia gets you in prison.
The only thing which would be immoral and unlawful by the CIA or FBI by attending a demonstration is if they proactively take part in it, fomenting an uprising by pushing citizens to commit unlawful deeds within the demonstration, fanning the flames...
Yep, that’s what I need, a HomoNazi supporting Foreigner telling me how Moral and Ethical the CIA is.