Well, if you don't put "public" then you can't share a permalink to that item with people outside the pump.io network (or even people inside it who aren't following you).

Given how many people in the world still don't have pump.io accounts, and how easy it is to use pump.io as a psuedo-blogging platform, I'll probably keep doing s/Followers/Public/ until the site learns to make that the default.