Religion in all its forms is a type of mental illness, but religious people will call it "having faith."
Having said that, people should be free to believe and worship whomever, or whatever they choose (feel free to worship a rock, a frog, or anything your mind desires) as long as you don't hurt anyone, or judge others for having different believes, or not having a particular belief. Sadly this is rarely the case (too many people have died fighting for their faith.)
At the same time, religion has become a business that in some cases can be extremely profitable (I won't name anyone out︀ of respect for their followers.)
*I hope I didn't offend anyone, but choosing to believe︁ in something or someone that only exist in your mind is a type of mental︂ illness, which is not necessarily a bad thing (I have a long list of mental︃ illnesses as well, being religious is just not one of them.)