Any empire is the "bad guys" pretty much by definition, but there are still bad guys and worse guys. And Ukraine is very different from Afghanistan or Vietnam - it's a country that's genuinely asking for US military assistance against an external enemy that invaded it for openly imperialist reasons (annexing territory etc). Not just the Ukrainian government, but when you look at the polls, it really is a "people's war".
Now, that still doesn't obligate US to help. But it does mean that any military assistance that US does render to Ukraine can only improve its well-deserved "bad guy" image. If you truly believe that US did an evil thing by invading other countries, what better way to redeem yourself than to help someone who is being attacked by a bully just like you?
Now, that still doesn't obligate US to help. But it does mean that any military assistance that US does render to Ukraine can only improve its well-deserved "bad guy" image. If you truly believe that US did an evil thing by invading other countries, what better way to redeem yourself than to help someone who is being attacked by a bully just like you?