Would we find it acceptable for people to making or using fake veteran's medals as fashion accessories? That would be the closest equivalent I can think off. The feathered headdresses of the Ojibwe, Lakota, and other Plains American Indigenous nations are earned, precious items. It was illegal within living memory for people from those nations to wear them - or any traditional clothing [until the 1970s, American Indigenous religions and all related items were illegal in the US], people from those nations are still being fined for wearing them in some places.
Surely, people can see the resentment it causes when the very people for whom this is a great honour not being allowed to wear them while others treat them as toys particularly for those who suffered through residential school period where their White teachers would make them wear fake ones out of sticks and feather bits to show how horrible their traditions were to try to "kill the Indian, save the man"].
When it comes to white dreadlocks, there is no historical usage of them in Europe - the Celtic glibs involved adding things to the hair to matt their hair together which is nothing like dreadlocks. The main issue with these is how often the current lived experience of people being fired, fined and more for how their hair grows naturally out of their head [yes, there are still employers that fire people for it] while White people at the same company can be treated as eccentric. That's before getting into the repeated issues in the media, including the last year, where Black celebrities wearing their hair naturally got destroyed, said they smelled of pot while White celebrities doing the same were praised for their 'creativity' and 'creating new hairstyles'. Until both groups are treated the same - until everyone can grow their hair naturally and wear them, there will be resentment when White people make fake matted-dreads without the same problems that Black people face.
Cultural appropriation is when one groups enjoys taking another group's traditions, important items, and/or physical features that are historically and often continuously denied to group it came from -- which causes a lot more resentment than being told 'please don't' a few times unless one think everything should be theirs for the taking. The division is caused by systems our society is built and continues to be supported on where some can get away with murder and be celebrated for dancing in their victim's clothes while the victim's family's are blamed for dividing society for having an issue with that.