Honestly I can't see how anything of
  this is problematic for anyone

Perhaps they heard about Brave blocking ads and... replacing them with different ads [1] that Brave makes money from.

That pretty much means the ads-are-cancer crowd don't like them, and the adblockers-are-theft crowd don't like them either.

[1] https://www.computerworld.com/article/3284076/web-browsers/b... https://www.wired.com/2016/04/brave-software-publishers-resp...