the person being an asshole probably needs medical help.

The first thing I was taught while taking psychology is that having a mental disorder is never an excuse for bad behavior.

First of all, there are plenty of people with mental disorders that do not act like assholes. Being mentally ill does not remove personal responsibility.

Secondly, trying to shift the blame from the person to their disorder only serves to create further stigma around those with mental disorders.

For instance, just because someone, who happened to have schizophrenia, murders someone it doesn't mean all people with that disorder are dangerous. Just because someone becomes violent when they are drunk doesn't mean all alcoholics are violent. We need to get over the idea that having a mental disorder excuses shitty behavior because it doesn't. Regardless if someone is mentally ill or not should not excuse them from taking personal responsibility. If they are that mentally ill that they cannot function then they shouldn't be in the general public alone.