It doesnt though, thats the point.
Its the same as competition in a capitalist marketplace. A company can sell terrible products and what should happen is people see they are terrible products and vote with their wallet to stop buying. Then the company goes out of business.
With free speech if somebody is saying something that other people think is terrible, they should stop listening to that person. They are still allowed to say anything they want, but their reputation is tarnished and hardly anybody listens to them and they loose their platform/influence.
In reality, people are weak and do not do these things. They keep buying the terrible products because they dont want to have to think about looking for a better alternative. They keep listening to the hate speech because its easier to respond in anger than to ignore the person. The solution to all these things is education and people spending more time thinking about how they respond to things in the world. Again in reality this wioll never happen, and so people will keep shouting and shouting about what they dont like until the world ends up destroying itself through hate and anger.