The intent of all the stack-exchange sites is to provide a high-quality resource of _answers_ for specific _questions_. If "the answer" to a question ends up being a divergent discussion, then not closing responses invites more of these types of questions. Over time that will subvert the intent of stack-exchange.
The POV of the stack-exchange folks is that there are plenty of forums for discussion, and that is NOT what they want to do. Hacker-news, however, is more free-form and definitely much better for "need advice" type questions with highly subjective answers.
That said, it is true that moderators sometimes get persnickety about what they close. I wish that at least they would be less smug and judgmental about how they do that. But oh well, it is still an awesome resource.