It sounds like you cared more about being right than from seeing it from his perspective. Even if you ARE right (keep in mind that right is often incredibly subjective), it's far more important to understand why someone is taking the "wrong" stance. Now, I'm sure you felt quite a bit of frustration over this and possibly other arguments. I'm not trying to dismiss your feelings, but once you understand someone's perspective, you can often turn an "asshole" into a colleague you can work well with. Believe it or not, being "right" all the time doesn't actually garner respect as much as being able to work well with others.
Whilst I agree you should always try and see things from the other person's perspective, and that this method often works well, I do think some people - some select individuals are beyond reaching.
Like an old manager of mine who told one of my team members in her review, "I'm not giving you a pay rise, but it's not because you're black." I mean, what can you say to that? She was in tears. The guy was so self-centered he didn't even realise that the things he said might cause offence.
Could it be that he didn't care more about being right, but rather didn't want his name attached to a project using deprecated crypto standards? Or that he genuinely cared about his customer's data security and privacy?
To me, he sounds like someone who's very defensive about a topic at work because of the conflict involved. And until I have reason to believe otherwise, I'll assume it's because of one of the two reasons I mentioned above (or both).
