But the Civil Rights Act of 1964 just outlaws explicit discrimination against people on the basis of their race or gender, and creates some bureaucracy to enforce this.

You might think this from reading the text, but that is not how it has been interpreted. Title VII has also been interpreted to address disparate impacts, which are not explicit discrimination. (it also outlaws discrimination on religion and national origin in most sections, and only outlaws sex discrimination in Title VII, not in any other part of the act.)

To your first point, fair. I think the crux is just very object level assessments of the individual speakers and the ideas they hold, and I don't want to go down that road here.

To your second point, your argument seems to imply that it is ok to exercise influence by calling people "racist" anywhere you can. That seems to imply that literally nothing would be "cancel culture" to you, which is not where you started a couple of comments ago.

I think it's fine to have a narrower idea of what views should be platformed within your own community than in society at large. Different communities have different purposes, and different purposes will point to different sets of ideas and speakers to be platformed. That is as it should be. I want to suggest two other possible cruxes which do seem somewhat cruxy to me:
1. deplatforming these particular speakers is not what the ideals of EA dictate. The core thing that EA is about is creating an intellectually open space to explore strange fringe ideas about how to make the world better, and these speakers fit that purpose.
2. Manifest is not an EA event. That is part of what attracted me to it. It belongs to the forecasting community, which is a distinct thing, even if the membership is overlapping. So when EAs try to deplatform speakers at Manifest, they are reaching out beyond their own community and trying to dictate what can be said in someone elses community, which sure makes it look a lot more like your idea of cancel culture.

Thank you for your explanation. One thing that stands out to me is that "human biodiversity" is a phrase that uses the language of science, yet you seem less interested in the scientific questions and much more interested in the policy questions. To continue with your example of Asians in the NBA, that seems to point at any number of purely factual scientific questions that could be explored. Are Asians generally lacking in some relevant physical characteristic, such as height, agility, or reflex speed? Are they better at something else, creating higher opportunity costs for them, and if so, what and why? Yet your seem to focus less on these scientific factual sorts of questions, and more on how we should respond to the observed difference on a policy level. Am I correct in reading that HBD is more a policy stance than an area of science?

I think the problem with making the hypo more concrete in the ways you suggest is that then whether the hypo represents reality becomes highly contestable, and we devolve into object level debates. To take one example, despite being very pro-immigration myself, I find your suggestion that deportation of non-citizens somehow violates fundamental human rights to be absolutely ridiculous. If you set up a hypothetical about Alice wanting to deport non-citizen Bobs, you won't convince me of anything. I'm guessing a lot of the disagreement here is less about event norms and more about people in the EA community being intolerant of those they disagree with politically. One reason for choosing such an abstract hypothetical was to try to separate out the two.

Can you tell us what you mean by HBD? Like give  definition? Is it just the idea that there sometimes are statistical, genetic differences between groups, such as racial groups?

Bob can attend or not attend for whatever reasons he wishes. I'm not trying to judge that at all. The question seems to be whether Bob can reasonably ask the organizers to deplatform or uninvite or ban Alice. In your scenario, I think the answer is "yes", though I would frame that as being about Alice's likely future criminal behavior, not directly about the belief that precipitates that behavior.

In this case, I think the "physically attack and maim" part makes it much more than just a belief. So far as I am aware, nobody thinks anyone under discussion in relation to Manifest was ever likely to physically attack anybody.

I think this concept of an "exclusionary belief" is incoherent. If Alice is a speaker at an event, and holds belief X, and Bob is very put off by belief X and is therefor less interested in attending, that is never just about X. That is always an interaction between Bob and X, it is a function of both. And for any X, there will exist a Bob. There are many anti-nuclear and green energy activists who would not attend a conference with a speaker who has advocated nuclear energy as a necessary part of the transition away from fossil fuels. There are surely researchers who do gain of function research, or who view it as essential to protecting against future pandemics, who would not attend a conference with a speaker advocating against gain of function research. I can certainly think of people in the world, on both sides of the political spectrum, who, had they been invited to Manifest, that would have given me pause. The question is how should we respond when we find ourselves in Bob's shoes? And I think we should definitely not demand that Alice be deplatformed. Asking for someone else to be deplatformed, because of our own feelings about them or their beliefs, is controlling behavior. It is a heckler's veto, and therefor contrary to ideals of free expression and intellectual inquiry. Ultimately each of us is responsible for our own feelings. Each of us can weigh the features of an event that we like against the features we dislike and decide for ourselves whether it is worth our time and energy and money to attend. Either choice is fine. But nobody owes us an event with any particular speakers or ideas included or excluded, and to act as though they do is just poor, controlling behavior.