Because if we don't, Russia will show the world that might makes right. And China will take Taiwan, etc.
Like peace in society, international peace exists because aggressive elements make an economic calculation, and stay calm. Once that math changes you get riots and wars.
Like when the US gave stingers to the Afghani, we don't support Ukraine for moral reasons (perhaps partly) but mainly because it's in our interest.
To be fair, might absolutely does make right in international politics still. The only reason we are even talking about Ukraine is that the Russian 3-day invasion totally failed and open up the opportunity for the west to sanction them and support Ukraine.
It weren't for that fact, the ability for countries like Germany to trade oil with Russia still would have totally overridden any possibility of sanctions.
And the West very frequently does not get involved in areas where terrible things are happening so long as those areas aren't really in their interests.
Which doesn't justify Russia in any form shape or way. Personally, because it's individuals we aren't involved in international politics and we are still perfectly valid in criticizing Russia for being hilariously evil.
And because in the world of might makes right, Russia is also losing.
So it doesn't really matter. Any Russian who tries to make this argument might be correct in calling out hypocrisy, but their weak and stagnant nation lacks the might to make the right.
Like peace in society, international peace exists because aggressive elements make an economic calculation, and stay calm. Once that math changes you get riots and wars.
Like when the US gave stingers to the Afghani, we don't support Ukraine for moral reasons (perhaps partly) but mainly because it's in our interest.