John Stuart Mill 'Utilitarianism'

[HnauHnakrapunt]

http://www.gutenberg.org/ebooks/11224
http://www.gutenberg.org/files/11224/11224-h/11224-h.htm

In a nutshell: human beings like pleasant things and do things that are right morally because they hope to avoid unnnecessary suffering.
The language here is far from being simple (19th century guy writing 18th century style) but when you find a quiet place to read it - it makes sense.

https://www.youtube.com/watch?v=-a739VjqdSI