What would the modern equivalent of this be? At least according to Chief Justice John Roberts white people have no legal privileges and legally sanctioned segregation is a thing of the past. So (according to conservatives) all of the racial differences in the USA today are artifacts of historical legal separation and personal racism. According to Roberts and others, people are making up legally sanctioned racism in order justify their circumstances. So if I changed my legal status to Black it wouldn't change my historical position of having ancestors who benefited from slavery and Jim Crow and it wouldn't change how I am treated by white people around me because I still look white. I think giving up whiteness and "becoming Black" today would need to involve something that would be a risk.
What would John Brown style allyship look like today?
I see Medium writers like Tim Wise and Walter Rhein deliberate provoking white people by declaring their allyship. They get attacked as race traitors. Robin D'Angelo and her white lady anti-racist types get attacked as well. Ironically, it seems these modern day would be John Browns don't seem to get much love from Black people either. They get accused of making money off of race. It makes public militant allyship not look that appealing.
In the George Floyd protests (in Minnesota at least) there were a lot of white people on the front lines. There was a concern by many anti-racists that left-wing violent radical white people were actually making things worse by making the movement look bad. But I watched enough live stream to know that most of the white people were out there and just as mad about racism as the Black people and were not trying to hijack the movement.
In both cases white allyship seems to draw attacks from both sides, and sometimes those attacks are legitimate.
The attacks from the right are legitimate because white anti-racists are dangerous to their united front. John Brown was a martyr and his death was one of the precipitating events that led to the election of anti-slavery Republicans and the Civil War.
The attacks from the left are legitimate because white anti-racists are not immune to patterns of white supremacy culture. White people have patterns that we cannot see because those patterns are the water we swim in. Sort of like men cannot see when we are man-splaining. White people cannot see when we are white-splaining.
So to give up being white today seems to look like backing Indigenous and Black and Latinx leadership. It seems to look like being a visible ally like Tim Wise. It seems to look like investigating how "whiteness" patterns show up in public spaces and deliberately acting differently. It seems to look like listening when people call you out and trying to learn rather than getting defensive.
Sometimes there are ways to use one's white privilege to undermine whiteness. I have access to audiences who might listen to me differently because I am a white man.