Tigers are so bad I've even met a bunch of fans that would be content with the club folding to stop the embarrassment. But is feeling embarrassed a Mental Health issue? They may be mistreated, but Tigers fans seem level-headed.
Parramatta fans get so into brief moments of success they have this weird sense of grandeur. This delusion is definitely a mental health concern. They also proclaim Gutherson 'King' which clearly shows their judgement is severely damaged.
Raiders fans may have mental health concerns, but it's more from the majority having to live in Canberra. But when they go mentally ill, they go hard - look at skeepe.
Warriors fans are kiwis. I'm not sure if that's a mental health issue or not. Either way it's generally entertaining (except for their victim complex).
It would make sense for Titans fans to be mentally unwell. How many underperforming clubs will they have on the Gold Coast. But then they get to escape to their beaches, so there is at least a healthy outlet. I'm sure all 10 of their fans are doing ok.
Knights fans are loyal as you can be, even when the club doesn't deserve it. I would say it's textbook Stockholm Syndrome, but if you've spent much time in Newcastle, it makes sense why they'd go to the games. At least they've have success in the last 30 years.
Dragons fans - still clinging onto the glory days of the 1960s, praising players despite despicable off-field actions, and are known to have well-known neo-nazi as a fan. Then there are the Steelers fans that still cling to hope that their club hasn't been completely eradicated (it has). Similar to Eels fans, it's this weird delusion that has encapsulated the fans.
So to answer the question - all NRL fans a mentally ill.