The Oatmeal sums it up nicely: autocorrect hates you because you don't give it any credit. We have all these sites full of screenshots of funny things that people have said, and blamed autocorrect for making it funny and making them "famous".
Autocorrect is like the sound engineer at a concert. No one really notices him, no one gives him any credit for his work, and no one cares about him, unless he messes up. The moment there's feedback or a mic cuts out, everyone shares their hate for the sound engineer.
If you have good writing skills to begin with, and actually type out the words properly, autocorrect does a nice job of helping you not worry about typo's. When you're typing on such a small screen, it's very nice to not have to worry about capitalizing certain letters and adding apostrophes and such. The lazier you get, the more your proper English breaks down, the more autocorrect has to work to understand what you're saying.
Autocorrect is also nice when you're new to a language. I have the Dutch keyboard on my phone for those rare moments that I feel like writing in Dutch. My spoken word and understanding is okay (though my grammar is a farce), but spelling is a challange. With autocorrect turned on, I've been learning the proper spelling for words and improving my overall skill.
Sometimes, I think it would be nice to have autocorrect give you statistics. I don't know what kind, but just some way of saying, "Hey, look, your typing is improving and you're relying on me less!"
In the end, the key thing that would solve everyone's problems — even if it made some websites of mistakes useless — would be to proofread your text messages! Every single mistake could be avoided if the sender would have just read over what they were going to say before hitting send. Sure, that takes a second or two more, but you don't need communication to be instantaneous. If you really did, maybe you should make a phone call and stop whining about your phone improving your shoddy English skills.