There’s one legit argument and it’s the principle of an agreement between nations.
How that is labeled not legit is nothing short of bizarre.
The same applies to NATO expansion eastwards, proliferation of missile defence and intermediate missiles and so on.
Bottomline the source of Ukrainian problems now is a foreign sponsored coup removing a duly elected leader and capturing power by a group which is not at the least supported by half of the country.
It is wrongly portrayed as a Russian-Ukrainian conflict.
It is not without parallels in history. Moldova is a nice example for them down to near a minor detail.
Now broken and abandoned by all parties after ‘European choice’ played. Officially the poorest nation in Europe.