The problem with banning hate speech is that the definition of what constitutes hate speech isn't agreed upon. The definition of hate changes based on the particular worldview that the individual subsribes to. By enacting hate speech laws, you've opened a pandora's box where political parties will weaponize it to shrink the overtone window and destroy their political opposition.

Furthermore, the only way hateful idea's can be weakened is if they are confronted in the open. If you ban hate speech, you will strengthen hate and create a black market of ideas where people are lured to hate simply because of its forbidden nature.