Yeah, Cersei is only dangerous in that she's a wealthy person with a mean streak a mile wide. It's the same danger posed by a petulant and self obsessed child with a loaded gun. Potentially lethal if you happen to be standing in the wrong place, but there's nothing subtle about her and she doesn't have the awareness to see beyond her own personal little world. Joffrey was basically Cersei turned up to 11 and with none of the social restrictions that comes with being a woman in this world that may have (outwardly) tempered her somewhat. I don't remember if it's been mentioned in the series, but I recall in the books that as a child she used to physically torture Tyrion as a newborn. That's seriously, grade-a messed up sadism.