Brian Cuban, the brother of Dallas Mavericks owner Mark Cuban, believes the holocaust denial groups on Facebook are unacceptable.

That's why he demands removal in this letter to Mark Zuckerberg. He writes that these groups help spread a message of hate.

This Facebook group denies the Nazis used gas chambers to kill Jews, and that holocaust stories are a myth created by the Jews themselves .

Yesterday, Facebook removed two Holocaust Denial Groups. But at least 3 are still up. Facebook Spokesperson Barry Schnitt says denying the holocaust is not a violation of its terms. However, protestors say even though not every website with hateful content can be shut down, Facebook can take a stand.

The social media website did recently remove a KKK group, and justified it by their terms of service which forbids posting hateful content.

Now, the question is whether holocaust denial is a violation of the terms of service as well, or an expression of opinion.