I disagree. I don't think SE turns people off when questions are closed, or discourages people from asking another question. Sometimes, you'll see a closed question asked by the user who go their question closed come up in meta, and the user will receive very constructive feedback.

The SE community works very hard to keep things on topic. The questions that come up on Hacker News are very interesting, but often times fit the definitions of being off-topic or not constructive. I don't think their closure has had any effect on the frequency of those really interesting off-topic questions.

Also, imagine if SE allowed these types of questions. The community would be overrun by flame wars and turn more into a discussion board, not a place to get answers.

On the other hand, I don't think closing questions has a strong enough effect to discourage people from asking off-topic or otherwise poor questions (see the Programmers.SE board for an example). It's been going through Eternal September for a couple of years now. (I'm not going to give an example of, what is in my opinion, the best moderated SE board since I don't want it to get any exposure and suffer the same fate)

So in closing, there's rhyme and reason to SE closing questions, and I don't think it hurts the site.