A lot of websites will censor people if they are expressing ideas that can be offensive to particular people. Although I am very opposed to racism, sexism, and homophobia, I think censoring these ideas can actually lead to worse outcomes than letting them speak freely would. Silencing these ideas will prevent them from being discussed with people who disagree. This will make the answers to their controversial questions more rare and less readily accessible.
For example, if somebody believes black people are inferior to white people, I feel like we both deserve the opportunity for me to prove them otherwise. Yes, often-times these types of people are closed-minded, but that doesn't necessarily mean they can't be convinced to change their views. It just means it will be more difficult.
Preventing these people from exposure to opposing arguments only reassures them that they're correct. It also may anger them, encouraging them to associate with others who hold the same beliefs and who are also angry. What this does is divides them from the rest of society. This makes them feel unfairly censored and makes them more likely to be more aggressive about their cause, and it can possibly even result in violence.
I'm also a firm believer in free speech. There were many ideas in history that were considered controversial or offensive that are accepted in modern society. Among them: abolishing slavery, women's rights, homosexuality, atheism. As evidenced by our history, many things we consider wrong or controversial could very well end up being accepted or even respected in the future. Because of this, I don't think it's fair to silence someone just because their beliefs don't blend into our current standards social norms.
HOWEVER, I do think the final choice of whether or not to censor controversial opinions should be left to the owner of the website or property. My opposition toward censorship is a purely moral discussion, and I don't believe the law should tell private companies how to run things. This is purely in context of morality and laws regarding public property.