This is a perfectly sensible way to do things. The concept that a person's politics is so "evil" that their talk acceptance must be rescinded is, frankly, child

This is a perfectly sensible way to do things. The concept that a person's politics is so "evil" that their talk acceptance must be rescinded is, frankly, childish. It treats attendees like small children, who can't rationally deal with the situation of a person with opposing views. Of course, if a person promises to speak on a technical topic, and then goes on a political rant, that's a reason to shut them down or walk out: the audience isn't getting what was expected and promised. But the mere fact of a person's unrelated political views being used to remove them from a speakers list - this is the sort of thing that you would expect from the USSR.