Mental illness is a very broad term. Plenty of people struggle with some type of mental illness but are still capable of using good judgment, making good decisions, and being responsible for their actions. To whatever extent McCants struggles with some type of mental illness, I highly doubt it has caused him to say all the things he has continuously said or that it justifies what he has said.
Also, just because people have criticized McCants for saying the things he has said doesn’t mean they don’t want him get help to deal any mental illness he may have and hope for the best for him in that regard.