I'm with Google on this one
Admittedly they're using latency as an excuse for saving the costs of transferring everything over https, but if the vast majority can't be arsed to turn on http, why should Google turn it on by default.
If you're storing or working confidential docs using Google, and using GMail for business (you're an idiot if you do) and you're worried about the security involved, then you already should know to turn on https. If you don't, you need to be clubbed to death with your keyboard. They're providing a free service, and are attempting to keep their costs down.
The Royal Mail doesn't have a bloody big sign on every letter box saying "Remember to seal your envelopes before posting so that evil people can't read your letters.". Same thing goes for postcards, you don't send the design for your cold fusion reactor on one.
Not that I use GMail or any of their services other than email, but if I did I would turn on https.
"Ignorance is not an excuse". Now, write it out a hundred times, and if it's not done by sunrise, I'll cut your balls off.