I think it's not just about balance.

The fact that an immoral idea can be spread should never, in a democracy, be an argument against whatever it is that spreads it.
That's because it's the people that are the ultimate authority and listening and spreading ideas is part of that process.

If the government pass a law to decide what idea can't be allowed, this is against democracy. And even if almost all of the population agrees with this norm, approving it would, similarly to electing a dictator, hamper democracy for future generations, who didn't get to participate in that decision.

The limit to democracy shouldn't be freedom of speech. It should be destroying democracy itself.