This is always an issue with racism...
it is true that every case has to be viewed on its own merits, and yes, sometimes someone idiots kill regardless of colour, so a black death isn't always the result of racism...
However, that is a joker card that is constantly pulled out of the hat in face of any racist incident. But we aren't talking about a street fight between drunken idiots and one of them happens to be black. We aren't talking about a self-defence situation which results in a death of a black man...
We are talking about two men who armed themselves (as you do) and actively sought out what they claim to believe was a suspect...
a) They armed themselves
Already they prepared themselves for confrontation. Even claiming a weapon is for self-defence still presupposes you envisage an encounter.
b) They had ample time to spot the suspect and call police, but failed to do so.
c) They had ample time to approach the suspect in a civil manner, but failed to do so.
d) When approached by two men in a vehicle bearing weapons, it is difficult to believe they feared for their lives more than Mr Arbery did.
If they feared so much, they needn't have approached him at all.
Whether they intended to kill, injure, apprehend, or merely intimidate Mr Arbery, the entire onus was on them. If take a weapon, seek confrontation and it results in injury or death, you could reasonably have foreseen that danger and it's manslaughter at the very least.
I can't 'prove' it's racism. Do I believe it was? Absolutely I do.
Actually, I believe it's a mix of factors, of which racism was one.
When you combine vigilantism, a propensity for violence as a 'resolution' and racism - you end up with dead black deaths.
Racism combined with other stupid beliefs is still racism.