Here is an honest answer. The argument is that white people set the cultural (legal/social etc.) agenda, and thus what is considered natural or normal. When Whites, being a majority, adopt a particular cultural practice, it becomes what most accept.

To be racialized is both to be othered, in terms of who represents "normal" in society, and also to be excluded from power to a significant degree (based on race). Since white people set the cultural, political, legal agenda, what we all consider normal or acceptable behaviour and so on, we can't be "othered." We are at the centre of society, not the margins. Also, since we are at the centre, we have the power, writ large. Racism = discrimination (othering)+systemic power. 

I understand this, and agree with some of it. The truth is that in some contexts now,  CDN minorities do have power, and then they tend to discriminate against whites (often reflecting the reverse in their lives as a whole). People are people, and act as people do.