I'm noticing quite of lot of posts to Ask/Show that are basically people using HN as a blogging platform. Sometimes they're tech-flavoured AI slop wrapped around a few links - persumaby an attempt at SEO. Other times they seem to be posted by users who may genuinely think that this is appropriate usage. Or they're cheap rants. Mostly they seem to be posted by new accounts. It's not clear to me that a captcha mechanism would help with this.