Why should we bother with the "apostrophe of omission"?

I’m referring to the apostrophe that acts as a placeholder when letters are omitted in writing contractions, as in “don’t”, “what’s”, “I’m”, etc.

This usage seems to be slipping in online text, along with many other conventions, of course. But whereas I don’t want to see capitalization go away, I have a hard time thinking of a reason to fight the disappearance of the apostrophe of omission. What does it bring to the game, other than yet another opportunity to screw up?

More generally, where do you feel we should draw the line in the sand with respect to changes in the rules of language? With more people creating more public text than at any other point in history, the evolutionary pressures on language are bound to ratchet up tremendously. Mutations are far more likely to “go viral” now than even twenty years ago. Is this a call to man the barricades and defend the old standards, or do we just let linguistic natural selection cull the herd?