"Again, I am only half serious" (said two times...)

Why say that at all? Is it a way to fend off ridicule? Or does this show a lack of confidence in the idea and what you are saying?

Reminds me of comments that start "Am I the only one who thinks that..."

I've gotten out of the habit of apologizing for things that I say or prefacing them with phrases such as that. The reason is that I found that it was a lazy way to not give as much thought to what I was saying and whether I needed to vet my thoughts more.