I actually disagree with you just a tad on this. While I do agree that Whitman wanted to speak out and be heard and also wanted others to do the same. His reasons for doing so include a more sociological issue that most educators and critics are afraid to talk about due to a lack of maturity in many students. As a 43 year old teacher living in today's times, I'm not afraid to discuss sexual orientation and do believe that Walt Whitman was gay. His poems make this rather obvious to me, and I therefore believe that he was closeted due to his era. Homosexuality was certainly an unspoken thing in the 1800's; he would not have been a well respected poet had this information been known. Allen Ginsburg wrote openly about his sexual orientation due to it being more accepted during his lifetime.
Again, this is just an opinion regarding Whitman's motivations for writing, and he is 'untranslatable' due to the times in which he wrote. He intended to be that way, using the majority's ignorance in his favor and to their disadvantage. I believe he hoped to reach out to others like himself, hoping for some sort of community development if you will. His poetry, in my opinion, was absolutely ingenious. BTW, not all of his poems were about this subject matter. He was nowhere near as obsessed with it as Ginsburg. Although, his era may have precluded him from being so. But wasn't that part of my point?
I often teach students that there are two meanings behind a poem: literal and figurative. Obviously, we will never know what was truly in the mind of someone who wrote over a century ago. But isn't trying to figure these things out actually what makes reading poetry fun?