I try to avoid the second definition altogether because the first is more interesting to me.

What we often hear is someone is disinterested meaning uninterested, and I do not like that application at all.

However, I think when I use "disinterested" for "selflessness," I am probably misunderstood in my intended meaning, so I'm careful with whom I use the term "disinterested." Know your audience; first rule of rhetoric. Besides, the word "selflessness" does the job better within the framework of what I guess to be most people's understanding.

wwh, in your quote above, I would take "disinterest" to mean "selflessness."