ya but in fact even Vegeta went through certain events which made him change.

but here it's like there are 2 different characters which look alike.
imagine Touma changes from the "nice guy-i don't want to hurt people" to the "I kill everyone-even though they gave up already" type next episode, without showing what made him do that.

if I remember correctly Lucia had a serious psychotic problem when Touma touched her, only because he isn't a member of her church.