They say sunlight is the best disinfectant. I think about that every time I hear about another protest against a speaker or an idea. If you really want to kill stupid ideas, you should actually let people discuss them publicly. Otherwise, they get pushed to the far corners of the internet filled with other nutjobs* There they get sympathy, not just for their idea, but for the fact that they were not allowed to speak publicly about it.
If someone wants to give a controversial talk, like to say that women are less intelligent than men, or that the Holocaust never happened, or that one race is genetically inferior to the other races, the best way to marginalize those ideas and highlight how stupid they are is to let them speak. Don’t even waste time on protesting the speaker. Don’t cancel them. Shrug and say it’s not even worth your time to fight, or, if you do want to fight, go listen to the talk and write a summary online about how idiotic the talk was.
The way to defeat ideas you don’t like is to make them compete in the public domain of ideas, not to censor them. When you censor them, you think you are squashing them out, but you are just giving them protected time and space to grow and find more supporters.
*if you are reading this at some point in the future, it is quite possible that the term “nutjob” is politically incorrect for some reason, but as of the date I am writing this it is within the bounds of things you can say, so please don’t crucify me in 2035 for writing this in 2020.