I don't want to be a friend to someone who has life and possibly mental problems
What is it about those conditions that would deter you from being friends with them?
I don't really want to spend my time with a person who is mad.
Just because someone who battling through mental illness does not mean that they are any lesser of a human. If you know someone who is going through issues like that, it would be the brave thing to do to be supportive to them.
Why should I?
Because people with mental health issues are still capable of being good friends. There is more to them than just their mental health. You won't ever find this out unless you give them a chance.