Of course the Russian people are morally responsible for their culture and its products (including the war in Ukraine). That culture has produced the conquest obsessed Russian state (including Putin, he is a product of that culture). The Russian people have reveled in the atmosphere of power, greatness, empire, return to glory, and all that bullshit propaganda that Putin has been feeding them for two decades. They cheerily rode the highs with him during the good oil years, applauding as he stripped away human rights one after another, refusing to go against him en masse. They now bear the moral responsibility for tolerating him from the very beginning (dictators quite often only get more difficult to remove with time). Oh now you can't get rid of him? No kidding. Oh now a lot of people would have to die to remove him from power? No kidding - like the people being killed in the name of the Russian people in Ukraine.
The Russian people are responsible for what ideas they hold, what they believe, who they follow, what propaganda they accept or reject (and they've been willingly drinking the propaganda by the liter for a very long time). They tolerated Putin's power grab and abuses for many years early on and did next to nothing to try to stop him. They have celebrated him often, he has been widely popular for most of his reign. How many more centuries of authoritarianism need to go by before people figure out that the Russian people are responsible for their culture and their culture is producing the authoritarianism. It's not bad luck producing those repeat results. Raise your hand if you think the Nazi ideology magically, spontaneously appeared - no, it was an assembled mash of ideas that were popular at the time, prevalent in the culture of the German region, commonly held by the people there. Putin's authoritarianism, his obsession with the Russian ethnic superstate (which is quite similar to Hitler's obsession with the German ethnic superstate), also did not appear out of nowhere, it's directly from their culture.
And - speaking as an American - of course the American people are morally responsible if their government does something similarly horrible as what Russia is doing in Ukraine. That very obviously also goes for what happened in Vietnam. The US Government and its presidents are the product of the American culture, which the American people are responsible for.
If the other empires of Europe changed (Germany, Spain, Britain, France, etc) - their people changed those empire, conquest obsessed cultures - then Russia too can and must change. Russia is the last major power in Europe still clinging to those decrepit, backwards ways. Russia must give up the notion of empire culturally and that means its people must fully abandon all the related ideas that propel and sustain that ideology (which endlessly spawns monsters like Putin (who is just another Russian Tsar type)). Until the people of Russia change their beliefs, the authoritarianism will just keep repeating.