People in general do not want to join anything else on the internet and keep up with another user name and password. Nor do they want to wonder how much information their Facebook or Google "login" will share either publicly or privately at a UNA site.

Years ago, I was using forum software which limited number of posts per 24 hour period. This is a cool feature for lonely people who post over and over about matters of little concern. A daily per-post setting would be a useful feature for anonymous non-registrants. For now, it makes no difference because only registered users can post anonymously.

No doubt, opening your site up to non-users can be risky.