Education.
Sell the idea to Carrottop. The resulting collect call commercial should kill the idea rather quickly.
Or, kill the idea by putting it into practice poorly. Ideas themself have no intrinsic value, their merit is based on their practical application (or lack thereof).
poison it through association with another, negative idea. For example, if you want to kill off the idea of “state’s rights,” you argue that it’s been used to support racism in the past.
How is Christianity and it’s monotheism better than Hindu and its Polytheism? How is Socialism better than Democracy? What ideas are good ones? Which are bad? How do you tell for an entire people, or do you? Does feeding a more socially acceptable idea into a populace weed out the unacceptable ideas? Is Mars red, or is it just the dirt?
Assign the idea to a special committee for its study. The reports and counter reports will drag on for years and possibly after the issue the idea addressed exists.