I don't think it's your right to tell anyone whether or not they belong in a conversation. The post was made on a forum in which I'm a user. That gives me every right.
You can try to marginalize the opinions of those that disagree with you, but that's not a rational argument against them.
Despite what your teachers and your parents may have told you, your opinion is not inherently valid. You have shown yourself to be ignorant of too many things to provide a meaningful contribution to this discussion.
If you have any comprehension of the racial history in the US and have to ask that then you really don't belong in this conversation.