There are many terrible ideas; the idea that the best way to police so-called "hate" speech is to repress it is a particularly terrible idea in a sea of terrible ideas.
Look. You can have a free and open society, or you can have a censorious environment – you can't have both, isn't that obvious? Do you want to live in a free and open society? I know I do. If you want to be able to speak truth to power then you're going to want to live in a free and open society. However, there are some consequences as a result – the first of which, that we all grow a thicker skin, stems from the reality that there are *always* going to people with ideas you don't agree with and some of those ideas you're going to find very objectionable.
The following points have been made over and over again but they bear repeating in light of the very bad idea that you're spreading.
(1) Banned/censored/repressed ideas don't "go away", they get pushed underground into an echo chamber.
(2) If you ban/censor/repress something then paradoxically you make victims – the purveyors of the ideas and others who support them will claim victimhood. The victimhood lends *legitimacy* to the bad ideas.
(3) Some people have conspiratorial natures and if you suppress something they'll think that there's something important "they" don't want us to find out about which gives the suppressed ideas an aura. Related is the notion of the allure of the forbidden fruit.
(4) Over time alternative platforms will spring into being to cater for the de-platformed ideas. We've seen this happen in real time recently. Thus censorship on YouTube/Twitter/Facebook/… has given rise to Minds/Gab/Dlive/Bitchute/… This is not new, in the past you had alternative presses and private presses. Look it up, let history guide you.
(5) All ideas need to be challenged, by forcing some ideas underground those ideas go unchallenged thus thwarting the battle of ideas in the crucible of reason (if you'll pardon my mixed metaphor).
(6) Contrarian types will naturally push back because of "who are you to tell me what i can and cannot read or watch or listen to"
(7) The whole *point* of freedom of speech is to protect the edgy and uncomfortable ideas. After all, when you think about it, anodyne ideas need no protection.