lol at 'too unsanitary'....how do you think the poor guys who have to get in there and unclog all the plugged sewer pipes from all the north american tourists who can't stomach not flushing their tp feel?
In Mexico, the general rule is, if there is a lined wastebasket next to the toilet, always put your used tp in there.
This does not apply to all hotels and many AIs, as they have their own separate septic systems. But if you go to a local restaurant or stay in a smaller hotel, you should not flush if you see the wastebasket or a sign.