Nakai isn't a character to simply sympathize or love. He's a symbol of the pathetic NEET otaku lowlifes who sometimes appear in real life. He's an embarrassment of society, a representation of human nature at it's most maladaptive state. Basically, he's an anti-shonen character. And because of his presentation, it provides an opportunity to think more deeply about Ohba's moral.
I see him as a test: If you can love him, you are a really compassionate person. You have the ability to love the old hobos who sleep at train stations. It's hard to see the point, though. Because if they haven't done anything good with their lives after 4 decades of life, why would they have any potential? Why would they change?
Just remember, even the most pathetic, rotten, and twisted of us are still humans.
On a happier note, HIRAMARU FTW!!! BEAT THAT FATASS!!!