Nobody says you have to abandon close friends that have made huge mistakes, you can help them through it while recognizing their faults - as long as they are doing the healthy thing in admitting culpability and working on positive ways forward.
What is generally ill-advised is telling the world that you are just going to ignore the mistakes or pretend they didn't happen so thay you can keep hanging with your deeply-flawed buddy. That shit's just unhealthy for all involved.