I think it is good to mention that a.) those with antisocial personality disorder (psychopaths/sociopaths as they were/still sometimes are called) utterly ar thought to be devoid of any empathy.
Enter ASDs. Lack of empathy isn't meant as total lack and it also has 2 components. There is affective and cognitive. The empathy that often is lessened or 'lacking' is the affective one. This also does not mean one can't sympathise. Another huge factor is the gender one identifies and how that affects one's ASD symptom demonstration.
The ability to mimic and girls often not being as encouraged to be loud/aggressive (esp. in play) makes for a difference that by now has started to be the subject of many an article/forum post.
Also, levels of anxiety and over stimulation plus any sleep deprivation will all lead to more 'numbing' in a way, heightened aggressiveness (even a little), impulsiveness and less empathic capabilities.
Actually, it's said that ASD causes a deficit in
cognitive empathy, but normal or sometimes above normal levels of affective empathy. Although the issue is complicated, and there is much disagreement.
Autist's Corner: Simon Baron-Cohen Responds to Criticism from an Autistic Blogger - Part I
There are individual differences among Aspies in regards to the degree of affective empathy, but such individual differences exist also even among NTs.
I personally think that the thing that distinguishes us is not that we all have too much or that we all have too little...I think it is that we operate in extremes. But what extreme exactly an Aspie is on depends on the individual. So just as one Aspie might have sensory
hypersensitivity, and another might have
hyposensitivity (or the same person might be hypersensitive to some things and hyposensitive to some others)...one aspie might never stop talking, another might never stop...likewise with empathy...some Aspies tend to be clueless in regards to what others are feeling, others are extra sensitive and perceptive. Some feel little emotional empathy, others feel a lot, more than others do. I feel no emotional empathy much of the time, but if something happens to one of the few people I really really love...I will be totally obsessed with trying to help them, unable to think of anything else.
I feel no empathy for bad news events but sometimes I will hear or read about less-publicised bad things happening to people I don't know (for instance the emotional trauma and exploitation of women who work in the porn industry, or the use of gentle pit bulls as "bait" for those other dogs being trained as fighters) and I will think of nothing else.
I felt no emotional empathy before the age of seventeen. Then I developed a little bit of it. Within the last two years, I developed a lot more.