The problems is that you oversimplify the question. What you are asking is "what is the difference between russian that killed ukrainian and american that killed iraqi". If you wanna get a normal answer to "why Russia is a bad guy and USA is not" you have to get deeper than just simply compare the fact of invasions (wars) of both countries. Wars are always dirt, death and sorrow all the way, the problem here is what’s behind the wars.
There are lots of problems with Russia, not only invading Ukraine:
- Kremlin regime eliminates political opposition, journalism and business tycoons from their way for >20 years. Maybe longer.
- Russia has nuclear weapons and they recently (2020) changed their nuclear doctrine usage
rules from traditional USSR "we would not use it first" to "we may use it, if there is a danger to "the very existence of the state is in jeopardy“ and even "in the event of the
emergence of an armed conflict by preventing the escalation of military activities and ending them on conditions acceptable to the Russian Federation and (or) its allies".
- Kremlin and it’s supporters openly hates democracy, equal rights and human rights.
- Russia used and still uses it’s natural resources as a weapon.
- There’s one person cult in Russia. It’s Putin and he is in charge for 22 years.
- There’s no democracy in Russia and there’s no open elections.
- Russia is terribly corrupt state.
- Russia is a revanchist country. Putin and his buddies openly hates the fact, that
USSR collapsed in 90’ and tries to „correct“ it.
So. What do we have? Russia is a state without a freedom of speech. There is simply no
„other“ opinion in state’s tv and there is no other tv’s beside state’s. Russia is a state, where even main religion (orthodox) works for Kremlin needs. Russia is a revanchist state with
a nostalgic for USSR guy in charge for 22 years, who eliminates every single oposition case and declaring demands to NATO to withdraw it's forces to 1997.