The diamond rule says to treat people based on what they want. Its biggest drawback is it gives no guidance whatsoever on how you are to determine what it is "they" want.
Hmmm... if only there was some way to determine what people want... some magical way to figure it out.
The misuse being ascribed to the golden rule is more often the use of the diamond rule.
You've got it exactly backwards. Example below.
It is the diamond rule that gives zero guidance on how to determine how someone else "wants to be treated".
Diamond Rule: "I'm going for coffee. Anyone else want coffee? If so, how do you take it?"
Golden Rule: "I got black coffee with sugar for all of you because that's how I like it. Oh, you like your coffee with cream and you're diabetic? Too damn bad because Jesus."
With no guidance, one is free to to use whatever approach one wants in determining how other person/people "want to be treated."
Look, just because you can't read the golden rule and pretend it says things it doesn't or can't figure out how people like their coffee doesn't mean the rest of us are so limited.