Because it’s disrespectful to blacks? Maybe he’ll be satisfied if they pledge themselves as slaves to black masters.
it’s controversial in two different ways.
First, it’s a ceremonial pattern and so cultural appropriation. (On the other hand, the patterns could also be considered the African equivalent of a Confederate Flag for reasons stated below.)
Second, the Ashanti have never been enslaved. Along with Nigerian tribes, the Ashanti became the largest holders and traders of slaves, gold and ivory on the Gold Coast. And, like the Nigerians who had over 2 million (internal) slaves in the late 1800’s, the Ashanti kingdoms had similar enslaved populations (combined, the most slaves in the world at the time). To use their ceremonial patterns as a stand-in for a people descended from slaves could be considered a huge insult.
an opinion from an Ashanti tribe descendant:
https://twitter.com/obianuju/status/1270053042340139008