I pretty much agree with everything earthw7 says.
The Creator gave different peoples different ways of doing things for a reason. Some of the rituals and ceremonies may be similar, but it is the differences that make them unique to the people who practice them.
HE has also set spirits in charge of both peoples and areas, and has taught the people how to call on them for aid.
When an outsider comes in and learns the ceremonies then goes and tries to teach it to others, then the danger comes in.
a person living in england trying to call on a spirit that is in charge of an area in utah is going to fail, because the spirit they are trying to call on has no authority beyond their area, and is bound to that area. Something may answer the call, but it will not be who the person doing the calling thinks it is. IF they are lucky, it will be a spirit that wishes to help, instead of one that wants to cause harm.
Taking care of ones family, then their people and strangers living among them, then those outside are constant teachings of the creator the world over. The ceremonies all differ though.
I could no more use a Lakota ceremony to accomplish a task, then a Lakota could use my ceremony. the ceremony will only work when conducted by someone who understands what it is for, how it works, and who has the spiritual authority to conduct it. some ceremonies can be shared, yes.
The Lakota ceremonies are not more contraversial then others, it is just they are the most widely copied, most known, so those objecting get more attention then others.
And when people claiming to be able to not only perform these ceremonies, but to teach others to do them.....for a price.....are confronted, then those who have paid money to the fake do not wish to accept that they were tricked, and lied to. They then will defend the fraud, even ignoring what they know in their heart is the truth, because they would rather convince themselves of the lie, then accept they were misled and deceived.