A significant part of the Sequencess is made of posts that argue for a singularity in the near future, with complete seriousness.

On the other hand in the early months of lesswrong the subject was explicitly banned. That was part of an effort to ensure that blog identified as about rationality and not "singularity with rationality used to support it".

We also have lots of posts about more serious topics. Having fun threads where we discuss HP and Twilight fanfiction doesn't mean that the community as a whole isn't trying to present itself at least somewhat seriously. And most top-level posts that are openly silly or non-substantive get heavily downvoted.

See the discussion on clown suits. I included scare quotes around 'sensibleness' deliberately.

I don't think Clippy reduces the quality of comments on the blog and I also don't think that discouraging Clippy for the purpose of appearing sophisticated would increase the quality of comments on the blog.