[Morendil]

Useless blog post: "X is a dumb idea, when we tried it Y happened which is bad."

Useful blog post: "We tried X expecting Z, but instead Y happened. I wonder what's going on, please chime in."

The mistake here isn't "negativity", it's Z-blindness. It's missing out on an opportunity to revise your model of how the world works, by noting that there is a discrepancy between your expectations and how things actually turned out.

(Of course, the "useful" approach results in less sensational titles, which may be why we see fewer of those.)