the judicial system, where victims have no rights and sentencing is a joke

Increasing human population

Negativity.

Greed

poverty /hunger without a doubt.

Religions.

A necessary evil-sometimes more evil than necessary.

I voted hatred because all the other 4 subjects plus many others not mentioned can be in some way attributed to hatred.

1. people are hungry all over the world for various reasons, some due to mass evacuations from war torn areas, some due to lack of work or the not having the ability to work.

2. Poverty can be due to lack of work, not capable of working due physical or mental issues and lack of adequate education.

3. IMO Religion is the second most cause of problems facing mankind, wars are caused due to differences in religious beliefs.

4. World leaders cannot communicate well enough to resolve the worlds problems, they are to consumed with helping their own country to really care about the global problems. 

5. Hatred is the biggest problem facing mankind, if people of all religions, races and colours could come together in friendship the world would be a much better place.

an extension of thinkin' of yoda's post

the unconscionable criminal conduct by a few over the many in the distribution of wealth

aliens