For the independence and freedom of their country and against occupation. These would seem like the obvious answers. But during any war, you’ll have ideological commentators trying to claim that the ‘goodguys’ are fighting for their ideals. The chief of MI6 claimed that maybe the most important values the Ukrainians were fighting for were LGBT rights. Yet now we’re being told the Ukrainians are fighting for democracy and the rule of law.  This is why the European Commission cannot reach a deal with Poland to finally give it access to the Covid recovery fund that nearly all the other member states have been given access to, because Poland is totally undermining the rule of law, while countries like Spain, the Netherlands and Sweden perfectly respect it. Really.
That is why nearly 2 million Ukrainians who support the rule of law and oppose Putin’s autocracy fled to Poland (which undermines the rule of law and follows Putinist autocracy apparently). It makes perfect sense.
No truly. The Ukrainians are fighting for their country’s democracy and the rule of law. An area in which it has excelled, unlike Russia, Poland or Hungary.
Whatever you think of the current Polish government, it hasn’t tried to ban 11 opposition parties, nor has Orbán in Hungary for that matter.
Now people might want defend Ukraine and argue that this ban is only in response to the Russian invasion (though South Vietnam wasn’t afforded similar leniency and attacked for not being a complete enough democracy during the Vietnam War and as such worthy of being abandoned), but problems with the rule of law in the Ukraine go back to before the invasion.
Presidents have been trying to kick constitutional court judges of the court for more than 15 years now.
The Constitutional Court ruled against certain anti-corruption reforms supported by the EU. This resulted in a constitutional crisis and President Zelenskyy actually suspended the court’s chairperson. 
Poland’s United Right government had that whole dispute were the president refused to swear in 3 disputed constitutional tribunal nominees and the Sejm nominated 3 new ones. This dispute about 3 judges has been used by anti-United Right parties in Poland, NGO’s, activist judges connected to the previous ruling party and the ECHR to reject the validity of the Constitutional Tribunal (despite it being of little consequence since 80 % of the current judges were nominated by the current right-wing government without any doubt as to their legitimacy because the Polish constitution allows a simple majority in the Sejm to nominate judges for the most important court). Yet the government never attempted to remove sworn in and sitting (and therefore independent and immoveable) judges from the constitutional tribunal. Hungary hasn’t dismissed judges from its constitutional court either.
Ukraine has one of the most unstable judiciaries and fragile forms of political pluralism in any European country. That doesn’t give Putin any justification to invade it, seeing how his country has devolved from a hybrid regime into a mere electoral dictatorship, but it does make Poland and even Hungary look like good stable hybrid regimes in comparison. Although Poland might not even qualify as a hybrid regime seeing as how the ruling party has only won two elections in a row so far.
Poland is doing more than any other European country to help Ukrainian refugees, and to withhold them aid because THEY supposedly violate the rule of law, while holding up the Ukraine as an ideal example of democracy, is like accusing Mongolia of democratic backsliding while praising China. Just no!
Hopefully Ukraine can develop a stable constitutional state which consistently respects the rule of law after it fends of Russia and peace develops in the region. But as of right now, the Ukrainian people don’t have a rule of law to fight for yet and we shouldn’t pretend that they do.
- Yushchenko dismissed CCU judges”. for-ua. 3 May 2007
- Zelensky suspends Constitutional Court chair for two months, UNIAN (29 December 2020)