Why do you write anything? I type way faster than I could ever write, and no matter how well you train someone in the art of cursive, most people's handwriting looks like crap.
So, yeah, I do write in all caps so that people can read what I write, but mostly I type.
And, now, for a thought experiment: If you were stranded on an island and wanted to be rescued, would you arrange your coconuts, sea-shells, and seabird carcasses in cursive? Would you use upper or lower or mixed case?