Two examples of when things go very wrong: Psychopaths and Fundamentalist.
Psychopaths are people who seem to lack any ability for EQ, or who’s EQ is so low that their malicious impulses and actions seems OK or normal to them. Psychopaths can have normal IQ (and sometimes very high IQ). Their lack of EQ could be a biological condition – they could be missing this portion of their brain and/or have damage to this section of the brain. They do not feel their victims’ pain (no empathy), despite a rational knowledge that they are inflicting pain.
Fundamentalist on the other hand can have normal EQ and normal IQ but they become so radicalized (by cultural or sub-cultural influences), that their ability to bring proper emotional consideration and rational thought to an ethical debate becomes highly impaired. These can be individuals on any point of the EQ or IQ spectrum; but through the process of being radicalized their cause seems so just, that any amount of damage to their enemies seems justified. Their intent is to inflict emotional pain on the other side; to avenge the emotional pain they feel the others have caused to them or their family/community/culture, etc. Their emotional frame of the others becomes rigid. The lens that they see the world through becomes warped.
A fundamentalist is IQ impaired because they will reject any evidence a priori (before thought/instantly) because it conflicts with their world view (personal frame or personal lens). In other words, no evidence that you present a fully converted fundamentalist will sway them. If something conflicts with their view, they will reject it immediately and give it no consideration. You can not prove a fundamentalist wrong because they know they are right; any evidence to the contrary is considered false; it has to be for them to be right.
A fundamentalist is ethically impaired because while they are using aspects of EQ & IQ to justify their actions, they fail to apply their own rules to the others. A fundamentalist can easily hold conflicting views in their head which somehow does not seem contradictory to them. The ability to hold the contradicting views in harmony is why fundamentalism is considered an abnormal mental state. De-radicalization of a fundamentalist is possible but is exceedingly hard and time consuming to do.
Of course there are less severe thinking malfunctions that can force our ethical compasses’ to point the wrong way. Long term examples would be cultures that condone maltreatment of minority members. Short term examples would be instances of things like emotional rage; usually triggered by some seemingly small offense which is interpreted as a large offense. The remainder of this section on ethics will provide greater insight into how good people can do bad things.