This generally happens when ideas presented in the conversation are radical and dangerous to a point the target people in the discussion feel an existential threat.

Look at the nature of this discussion. Presented in its simplest form, its a case for a merit based system. The socialist types don't like this, the very fact that merit is being discussed implies their entitlement to free resources at the expense of other hard working people is threatened. They can't allow it to go on.

You don't want people to start thinking about it.