Define Sarcasm and why do people use it

According to Wikipedia, sarcasm is "a sharp, bitter, or cutting expression or remark; a bitter gibe or taunt". Sarcasm may employ ambivalence, although sarcasm is not necessarily ironic. "The distinctive quality of sarcasm is present in the spoken word and manifested chiefly by vocal inflection." The sarcastic content of a statement will be dependent upon the context in which it appears.

My question is why do people use this style to communicate when it is unnecessary? It invokes negativity and promotes an hour equal response, so why do we do this to each other? Is it because it's funny? I find it sad :(

Check out my video on superstition:

Peace and love