I'm not sure if open borders today carry the same implications that they carried back in the 19th and early 20th centuries. Open immigration is a good thing but not without some parameters. Accepting devoted communists in the 1950s may have altered the course of America. Accepting numerous immigrants from any culture that is radically opposed to liberty - be it Islamic militants, socialists, or fascists - is not healthy if those coming are not fleeing prosecution but rather spreading it.
That said, Reason TV has an interesting interview with Grover Norquist on open borders. The issue is complex. Barricading the nation against 'invaders' is as bad as the government spying on its own people. It is tantamount to basing everything on suspicion. However, opening the borders wide and accepting all of the huddled masses is patently naïve in it's notion that everyone coming to America has good intentions. Norquist makes some interesting and reasonable points but the issue is not black and white. It requires a lot more thinking than the political sound bites we hear, that are driven by politicians with probably the same gut reactions and instincts one way or the other that everyone else seems to have.