I've only met one McKinsey employee that I actually liked. Even then, it took me awhile to trust him. He has since moved on thankfully. Not everyone that works there is corrupt, but their senior leadership sure seems uncontrollable.
I'm in the industry, and thankful that my firm actually goes above and beyond to avoid this type of COI. It's not been a huge secret that not everyone does the same.
Let's just say the companies that primarily use McKinsey at a C-level mirror some of the same shady practices, especially internationally where there is less oversight.