Speaking as someone who speaks about X-risk reasonably regularly: I have empathy for the OP's desire for no surprises. IMO there are many circumstances in which surprises are very valuable - one on one discussions, closed seminars and workshops where a productive, rational exchange of ideas can occur, boards like LW where people are encouraged to interact in a rational and constructive way.

Public talks are not necessarily the best places for surprises, however. Unless you're an extremely skilled orator, the combination of nerves, time limitations, crowd dynamics, and other circumstances can make it quite difficult to engage in an ideal manner. Crowd perception of how you "handle" a point, particularly a criticism, can do a huge amount in how the overall merit of you, your talk, and your topic, are perceived - even if the criticism is invalid or your response adequate. My experience is also that the factors above can push us into less nuanced, more "strong"-seeming positions than we would ideally take. In a worst-case scenario, a poor presentation/defence of an important idea can impact perception of the idea itself outside the context of the talk (if the talk is widely enough disseminated).

These are all reasons why I think it's an excellent idea to consider the best and strongest possible objections to your argument, and to think through what an ideal and rational response would be - or, indeed, if the objection is correct, in which case it should be addressed in the talk. This may be the OP's only to expose his audience to these ideas.