Languages developed from not having a word for something and trying to describe it. Because of this when we say something in English, its more natural for a baby to learn it since its similar to how their instincts would describe it.
It doesn't matter how much you sing me a song in a different language. I won't learn a single word and it's meaning in that language. You need to learn to associate the word with an object or action, hence holding up objects to your baby and saying the word of what it is. If this guy did not realize that, he is simply an idiot.
While I will agree that speaking in only Klingon as an adult will effect your social life, I fail to see how having Klingon spoken to you as a baby will impact your adult life in any way.
I cant speak from experience here, but from what I have seen, many Trekkies have great social lives. There is a huge active community for people who enjoy it and I am assuming they are very happy with it. Looking down on people who have different interests than you is so childish.
Also, if he did grow up to be a Trekkie and spoke Klingon fluently, I am sure he'd be a big hit with the Trekkie ladies. Jus' sayin.