No one disputes the human rights of black people. What
is disputed is whether police killings are racially motivated or whether American police are too often heavy handed irrespective of race (94% of Americans believe that some police reform is needed[0]).
Of course, virtually everyone understands that blacks are killed disproportionately by police, but that doesn't imply a racial motive when we know for fact that there are disparities in the commission of violent crime, rates of police interaction, etc which could also explain the disparity in shootings.
And of course, the particular remedial policies depend significantly on the answers to these questions. In particular, people who identify strongly with BLM are much more likely to advocate defunding or abolishing the police (but are also the least happy that inadequate policing led citizens to defend themselves during various BLM riots in 2020, including the Rittenhouse case).
Further still, there's a lot of controversy over whether violence or non-violence are the appropriate way to seek the reforms one desires, with virtually the whole of the media downplaying or actively justifying political violence (even invoking MLK's "riots are the language of the oppressed" out of context[1]) right up until January 6th, 2021 when political violence abruptly and rightly regained its "reprehensible" designation.
Further still, contrary to the media portrait, a majority of black Americans don't support violent protest or the abolition or defunding of police--like most other Americans, they want sensible police reform[0].
So yes, BLM is quite controversial in American politics for reasons which have little to do with clear cut advocacy for human rights.
[0]: https://news.gallup.com/poll/315962/americans-say-policing-n...
[1]: One of the more memorable examples was CNN adding the "fiery but mostly peaceful" caption as a journalist sporting a gas mask reported against a backdrop of a dozen burning vehicles.