Why do people use the word, "hate", so much?

The answer is because most average people these days have a poor repertoire of memorized words, and bad grammar as well. Further, most people do not know the word's actual definition and appropriate meaning. 
Yes "Hate" is a most overused and abused word. The other one is the F-Bomb, which is a noun, verb, adjective, and adverb for the illiterate and uneducated. 
(I should make a bumper sticker out of that)

I share your feelings about this, and whenever I can do so without upsetting people, I say, 'Hate is a really strong word; I'm sure you just mean you really dislike your teacher, or you think raspberry icecream is yucky'. A lot of children simply don't realise how strong the word is, and are interested in and receptive to being told other ways to express a strong dislike.

They have a poor vocabulary.

The same reason they must label everyone as either gorgeous or ugly, when in fact almost all people are ordinary looking. Part of it is lack of vocabulary (who reads any more?) and part of it is that adolescence comes with very intense emotions which young people must learn to sort out. That's why teens often have tantrums about mundane things. In their emotionally charged world, they do truly swing between extreme love and extreme hatred. However, they themselves realize that's not reality.

Maybe it became popular when George Bush started talking about how the  terrorists "hate our freedoms," as if that somehow explained the 9/11 attack.

It's the same as the word "love". It is used to express strong feelings, thus they choose a stronger word to express that.

Exaggeration and dramatization seems to be in style these days. People are using words like terrified, devastated, and panicked for events that are merely, in fact, somewhat upsetting to a normal person. I often wonder what such people will say when something truly awful happens to them.

Because of the shortness of the word. It's easy to say and directly communicates whats you want

Some would attribute the desirability of hate as a sign of negative perceptions that seem to elevate the status of meanness and unhealthy emotions like "hate."

often overused,,in informal conv among your  bffs,sharing stuff to grouse about is common,where the writer or speaker wishes to convey facets of a complex situation, this word and others become word fillers,mundane,dry,,,expediate, ( wrong,it is 'expedite') ,excetera,nucyuh ler,as per,true facts true history,past history,prior plans,prior history,future plans,various and sundry,excape,point n time,genral consensus,concensus of opinion,genril consensus of opinion. ( 'gen/rll' that is how bad word raconteurs make it sound) ,outer perimeter, loose lose,lossed lost,choose chose,,preboard prepay prequalify,prepay,preorder,preregister,regester, we'll,well,your,you're , would of,libary, to,too close proximity,general consensus,disorientating,nope nope,,origination,,nope,, word is origin,another couple, masonary,,as in bricklaying,,it is'masonry' not 'masonary'promissary,,as in 'promissary' note,,wrong,,it is promissory,,'promissory note'

these are heard and seen   in writings  from people from 16 years old to post grad college

"I am a Radical Leftist rabble-rouser, and if you disagree with me on even the slightest point, you are guilty of a HATE-cr!"

I'd be happy if they'd just stop saying "hate ON something." Hate is a transitive verb so you don't need to say ON. You just "hate something."

Each persons language and situation is different and language is fluid. 

I don't consider hate in every day context to be a strong word, but obviously you do. Right there is a difference that we have to respect.