When people spell out the N-word one letter at a time through a comment chain, who bears responsibility? Do some letters bear more responsibility than others?

Let's say you're a moderator and need to decide who to ban. There's no rule against posting single letters, but there is a rule against spelling out racial slurs. So do you just ban the person who posted 'R'? But by the time you get to 'E' there's no other word in the English dictionary that could possibly be spelled, so maybe you should ban 'E' as well. Or maybe you should just ban everybody?

I feel like there should be some analogous ethical dilemma, akin to the trolley problem.