The Russian propaganda part is that you act as if Russia is defending, while actually they are invading.
Do the neighbors of France need an alliance against a French invasion? Do the neighbors of Germany need an alliance against a German invasion? Why not?
Publicly available, historic facts do not support the argument that russia's invasion was legally justified under any reasonable interpretation of a "threat". Claiming that they do is the propaganda mentioned above. russia is, in fact, the invader, and Ukraine did not invade russia first.
Also, you should respond to the second part of their post, as it contains a viewpoint that you might find interesting, and a question asked of your own viewpoint. Understanding others' viewpoints is a good foundation for coming to agreement.
Do the neighbors of France need an alliance against a French invasion? Do the neighbors of Germany need an alliance against a German invasion? Why not?