Should a festival aimed at people of faith invite a militant atheist? And does there ever come the point where someone should be excluded for their views?

Yes, of course ... to both questions. Having a vigorous, intelligent debate, especially about something very important to us, is a great way to provoke us to think, pushing us beyond our often unexamined assumptions. Of course, when this is advisable to do is a different question--I would see it as part of a larger festival theme: perhaps one year the theme could be "Doubt" and you might have several debates or exchanges with people holding a variety of theological positions (atheism, pantheism, agnosticism, deism, personalism, etc.).

And yes, of course there are people so far beyond the pale of what most people consider decency that inviting them to engage is an easy "hell, no!" Neo-Nazis, white nationalists, those that try to jusify the use of terrorist tactics to further any political cause, racists of any stripe, antisemites, misogynists are not owed a platform by those of us who find their views repugnant.

I'm very much dismayed by Dawkins' advocacy for terminating pregnancies when it is known that the baby will have a disability--if that is, in fact his position. If he recommends aborting a fetus that is so disabled that the individual would die very young, or would never be able to perform most of the activities of daily living, that's one thing. But if he wants a sweeping policy of aborting all children with the likelihood of any physical or cognitive impairment, that is something else entirely. I would like to ask him what ethical principle he bases that upon--but that's a different discussion. Had it been up to me, I would have looked for a representative of the nontheistic point of view whose reputation was not clouded by Dawkins' other beliefs.