Do you think that......?

your reason is a very good one, but also, by using proper english/language makes one sound/appear smarter

examples: saying "going to" instead of "gonna", "want to" instead of "wanna", etc

Colloquial speech by its very definition is the use of words and/or phrases in informal conversation among where like/distinct cultures of sects of people communicate; it is not used in formal speech or writing unless translated for the outsider to understand.

This is how societies of people have communicated for centuries and essentially is how language was born. Our dictionaries are full of words which were initial colloquial and which due to extensive use have been incorporated into defined language. So yes it is accepted and represented in our history and poetry books to explain cultures and societies unknown to us to satisfy our universal quest to get to know the world we live and lessen the global gap.

No because too much colloquial speech, leads to the inability for some people to speak formally, and express themselves correctly.

Fo shizzle. I be using that jizunk all the tizime up in this piece right thar.

i say yes, so everybody feels involved

because of the lizards =]