Understand the Russian history, self and world view, reasons for their views, why they are concerned with NATO expansion, why they conduct their security as they do.
Ukraine is as much a justified defensive strike for them as it is an unjustified attack by most of the world. The public rationale are not the real rational and has been in the works for more than 10 years.
Putin has stated he wants to reunite former Soviet states.
Ukraine becoming more democratic and wanting to join western systems like the EU and NATO make that impossible for Putin.
Putin cannot afford a large successful Slavic democracy to be a direct comparison to the authoritarian regime he’s built. If democracy and free markets succeed in Ukraine, no amount of Putin’s propaganda will protect him from long term instability and potential overthrow by the people that have been under Russia’s corrupt yolk for 30 years.
Assuming that Putin's statements are representative of the Russian people is clearly incorrect.
Invading another nation isn't "conducting security".
You can use your line of reasoning to justify any action however evil or wrong as long as the person taking it is giving a reason in the meantime.
OP: How to argue that invading Ukraine is wrong?
You: Here's what Putin and his supporters think.
Sure, he's made public statements about this, I don't get how they're relevant here given his position. Every tyrant and aggressor in history has had a bullshit excuse and a group of supporters. That doesn't make their position equally good to the people they're opposing - and that's what I thought you were saying with your previous comment.
The beliefs are due to propaganda. Most Russians have close ties to Ukraine and would never think of waging war for no reason.
Ukraine is an independent nation that is not going to hurt any other country but only tries to improve the lives of their citizens.
Russia, or particularly Putin, has ambitions to force Ukraine to follow their lead. This was going to end and that's why Putin decided to attack. But his mental state that sees them as potential danger is wrong. It is a reality but still wrong.
We accept that people have different religious views. Is abortion completely wrong? Is it so difficult to see they have very different world views?
As for religious views – yes, it is wrong for one religion to attack another. Crusades are wrong, especially today.
Every country has more than 0 neo-nazis
fight on your own territory, fight on someone else's territory, the second won out but failed terribly and they were forced back into their own lands
Is this your real opinion?
I think it's interesting to discuss with people I disagree, because they may have a different point of view in some topics. I don't expect to reach an agreement in these topics that have a strong political and emotional charge, but I think it's worth having an honest discussion.
If this is not your opinion, the problem is that you may be misrepresenting their point of view. You many be holding a straw man so people takes turns to punch it. And the only takeaway is that anything can be misinterpreted if someone tries hard enough, that is hardly surprising.
Right now, I'm spending time gaining as many points of view as possible to gain understanding where I lack it. But it is obvious that there are many very different world views between the countries of the world and the generations of citizens in each.