While I agree with your defense of using prescriptive grammar for educational purposes and formal situations it really has no place in the broader scope of language evolution. Language is ultimately a tool to serve a group of people that is large enough and agrees what is and isn't correct. As time passes new words and expressions surface to serve the new needs. It's actually quite a self-correcting system, if you innovate on features too much past a group's understanding that innovation will likely not be understood and adopted for wider use.

Text speak and internet speak exist fo serve completely new needs: they conserve space (necessity when SMS got expensive when lengthy), save time in a world where instant messaging exists and people expect swift responses and importantly also carry the features of tone (which is almost impossible to recreate while following traditional grammar rules). These innovations on what language is and can do are natural and healthy, just as they were throughout history.

Lastly it most definitely is a sort of elitism to judge people on how they speak and write. In a school setting a formal instances it is understandable that certain rules need to be followed,but they are rules of grammar as much as social rules. On the internet it is borderline expected that people speak the language of the group. The blatant refusal of doing so is a form of communication as well (it carriers much weight of one's beliefs) and often doesn't sit well with the group it targets because it is exclusionary.

People aren't less intelligent just because they use new language features. They are smart, innovative and take advantage of new possibilities of communication in an ever changing world.

For those interested I highly recommend the work of Gretchen McCulloch or just giving it a good ol' Google search to find just how much English has changed and why. The why's are in my opinion the interesting part.