The real world.  Hmmm.  You say the marketplace of ideas is "the real world," and you imply it is therefore true.  Well, the "real world" South until 50 years ago was full of lynchings.  The real world of some Muslim countries allows the stoning of gays, even today.  Why?  Because in their marketplace of ideas, those ideas are the most popular.  Is it true that blacks should be lynched?  That gays should be stoned?  So there you have it:  The marketplace of ideas --- like any marketplace --- measures popularity, not truth.