Grammar "rules" try to force behavior on people, language is a form of expression, as long as those that you communicate with understand what you are saying, what difference does it make whether your dangle a participle or not?
There are some contexts (lawyers are a prime example) in which the form and function of words is very important, in most cases grammar is just a set of rules that some people that that they were better than everyone else arbitrarily set to paper.
All that being said, I want to reiterate a point that I am certain that some people will miss - It is important that the people that you are trying to communicate with understand what you are trying to say. The structure of language does make it easier for people to communicate across social and regional barriers, but there is nothing wrong with colloquialisms and regional dialects that "bastardize" the English, or any other language. There is nothing inherently good about proper grammar - grammar has a purpose, but its form is arbitrary.
And ain't IS a word, one that millions of people use on a daily basis, just because some grammar nazi decided that it isn't a proper word means nothing.