Dan, I don't think a person can actually block another on this site. On three other opinion sites I have been a member there is a blocking button and when you hit it, the person's comments either become invisible to you, or they simply can't comment to you.
I personally don't block people, but I know many others who feel more protected when they have that option.
I didn't know about the star symbol being the link to messaging somebody. Thank you for telling me.