When we tell people they can't use the site primarily for political or ideological battle, that's because the purpose of battle is to defeat enemies. One uses whatever tools and weapons one can, over and over until the enemy is defeated. Repetition, in battle, is key to victory. But curiosity withers under repetition. Curiosity looks for something new that hasn't been said or seen or thought before. Curiosity wants to encounter difference—ideology wants to defeat it.
Not only do ideological arguments on the internet tend to be repetitive, they also tend to quickly turn nasty, and that is another quality that kills curiosity.
You're right that I often tell people that a good HN user tends to comment on a diverse range of interesting things. But that's just a proxy for curiosity. If that's not how your intellectual curiosity works, that doesn't need to be a problem. What starts to be a problem is if you're using HN to push some sort of political or ideological agenda rather than to gratify curiosity. Users who do that have a wrong goal for HN—their goal is to bend the threads in the direction their agenda is pre-focused on. The right goal is to bend the threads in whatever direction is most interesting—and that tends to be unpredictable.
I typically post when I am reasonably informed about a topic and see representation for one viewpoint, but not the one I have. I also do this when existing comments are dominated by a single uniform perspective or feature one perspective repeated many times relative to others (groupthink). I view my postings in such situation as diversifying the information represented in a given discussion. Very commonly, I see these situations with single-viewpoint domination present themselves in topics that are 'political', and perhaps this is because the HN demographic (location, profession, and so on) is relatively homogeneous. And so I end up commenting in such discussions more often.
Additionally, I am less interested in some of the purely technical discussions (such as "why is framework X better than framework Y") and more in the economic/cultural/political discussions that take place here. Given time limitations, even though I may lurk on many different topics, I post on those few topics more often. Those discussions are inherently ideological in nature, and taking any position could be considered ideological. I don't understand why the litmus test for being a good HN citizen is "posting on several different topics" since that basically means one cannot participate or contribute without investing time significantly, or by artificially keeping up some balanced spread of contributions.
To bring things up a level - we all live our lives and contribute to broader society in specialized ways, since we all have different interests/values/experiences. So why require something more generalized and diffused by way of commenting?