A Causal Vacancy
Joe Polchinski takes up the subject of black hole firewalls in a guest post at Sean Carroll's place. I won't try to summarize his whole argument, except to say that one point is that several things generally believed to be true about black holes turn out not to all be mutually consistent.
The most annoying thing about black holes is that break down of space time at the classical singularity - call it the causal vacancy - my apologies to anyone who thought this might be a Jo Rowling post. The second most annoying thing is the (classical) non specialness of the horizon, which Polchinski calls the "No drama" hypothesis. Firewalls violate that idea.
I also like that Polchinski throws a bone to my favorite crackpot theory:
Actually, over the years many people have suggested that the black hole geometry ends at the horizon. Most of these arguments are based on questionable dynamics, with perhaps the most coherent proposal being Mathur’s fuzzball, the horizon being replaced by a shell of branes (though Samir himself is actually advocating a form of complementarity now).