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.