Reply #5: What you raise as a concern is not a free speech problem, but rather...

[Blackhatjack]

a problem with the officials in charge of the forum exercising good judgment in deciding who gets to address the forum audience.

You can address this problem by using MORE FREE SPEECH rather than less. You have the right to speak out on the inappropriateness of forum officials giving Ahmadinejad a platform from which he can speak.

However, any group in the US can invite any individual or group to speak as long as the individual or group is not subject to criminal prosecution and/or court order.

The SCOTUS decisions which allow groups like the KKK to speak publicly, march publicly and distribute information publicly have long upheld the right of abhorrent groups to be heard. But nothing they say is condoned by the government or the people just because we allow them to speak.