Religion can be a form of mental illness, as can any other set of beliefs allied with practices.

For example...let's take your definition of religion, "They can't all be correct , they're always fighting each other and they seem to be rich organisations." ....and apply it to (big drum roll)...

POLITICAL PARTIES!!!!   (da-da-dum!)

Now let's apply it to....

NATIONALISM!!!!!   (da-da-dum!)

Those are two more areas in life which are absolutely riddled with mental illness, in my opinion. :-) Whaddya reckon? Then there is corporate competition for market share, the adversarial justice system, and organized sports! More rich organizations who are always fighting each other.

The fact is, there is are sane ways and a great many insane ways to do absolutely anything, religion included. To single out religion alone is probably an indication of your own prejudices, not a comment on religion itself.