Antitrust and Marginal Revolution

Bryan Caplan asks under what conditions would the antitrust authorities prosecute me and Tyler?  When we raise our price?  When we require MR readers to promise not to read any other blogs?  When we merge with a competitor?  Or when we predate by producing so many high-quality posts at such a low price that it forces other blogs out of business?  (heh, isn't that what we are doing right now?)

As Bryan points out, raising price wouldn't cause legal problems but all the other actions would.  Why?