No stan is 100% rational because stanning is a delusional thing. I consider myself to be more rational than delusional, but of course part of me is delusional and gives my faves too much credit. I'm still extremely critical, though.
I'm just as quick to criticize my faves as I am to praise them, much to the detriment of some delusional stans on here. So would consider myself a pretty rational fan. I don't subscribe to the mentality that you're not a "true fan" if you don't think your favorite artist is God.