What kind of kindergarten level understanding of racism are you working with here?
When one group is dominant over another and seeks to solidify that dominance through power they did so by gatekeeping resources, dignity and respect.
It will allow members of the non dominant group to succeed on a very narrow path
They are also told that those who did things "wrong" are jeopardizing the acceptance of those who did things "right"
*Note: "Us" is only a permanent state for members of the dominant group. The assimilated can always become "them" again in a moment.
Doing so usually means standing with the dominant group against your former people
The desire to avoid this means the assimilated frequently overcompensate.
"They're doing it to to their own people"
The purpose of hazing is to raise the cost of entry to a group such that the person internalizes membership
"I wouldn't have gone through that if it wasn't worth it"
"I have to be loyal to and defensive of the dominant group I joined or else all that work and pain was for nothing."
For those who made it through all the hoops, it is easier to resent those who seem to get in without the same work.
Nobody likes line jumpers.
But like most exclusive clubs, the line is mostly for show.