Fanatically means with devotion so extreme it allows no other view. Fanatically loyal, fanatically tidy, fanatically opposed.
It is often affectionate about small things, since being fanatically tidy is a joke about somebody's habits. About beliefs it is not affectionate at all.
1adverbfanaticallyWith devotion so extreme it allows no other view.
“He is fanatically devoted to his football club and has never missed a home game.”
fanatically is a manner.
From fanatical + -ly.
Etymology from Wiktionary, CC BY-SA