Well yeah, no American civilian needs an AR-15. They live still in a democratic country and the US has the greatest military power in the world. They are oppressed by the government in their own heads. Things might change in 3 years with an orange Putin fan that doesn't recognize a democratic system and may have in place his minions to overturn an election if needed. I doubt that the American citizen will ever have to worry about the American military but looney militias like the Proud Boys and friends with AR-15 or whatever military grade overblow equipment they crave. And that's what Putin wants, to start a civil war in the US.
As for Ukraine, they are, like they've been in 2014 fighting back one of the biggest military power in the world beyond their military forces, having the citizens to take matters in their own hands.
I think it's easy to see the difference, so I'm gonna assume this is wilful ignorance.