Why do people fight online a lot?

I actually think that many of what we see as offense online is categorized as

1-people that had a bad day, exploding on strangers instead of taking it out closer

2-Miscommunication and misunderstanding, without visual cues conversations are blind to our emotions.

3- a
Trolls, people in deep pain taking it out on others due to lack of compassion around them
3-b
People that are genuinely mean. Those that where bullies at school or those that where bullied so much they became bullies online.

If the above is offensive to you I do not mean to offend. See you do not know me nor see my expression when you read my blog.
With compassion comes a wider understanding of our humanity and this is needed in the social media era, and the next era that will be born soon.