The word 'negativism' can be found in the dictionary. If you look up the dic you will find it means the same thing as 'negativity'.

IMHO: It is very important to have a few bad people in this world (People with rotten morals, people with a lot of bitterness, skepticism & thankless people). In other words 'negative people'...It is good to have them around becoz' how else can one appreciate the virtues/goodness in men?

If all men were good, kindhearted & forgiving in nature..nobody would appreciate these qualities in men.