Its not assisting a thief is it robin?
Its letting a bit of air in the car on a hot day?
Nobody is saying they leave the window open to 'assist a thief'!
Totally off topic now end of.
....The topic is about leaving windows down and alarms. What are alarms for? - To alert you to some scumbag trying to get into your car uninvited. If scumbag sees a window gap, surely it presents him/her with an added option to gain entry. Whether you like it or not, it is your responsibility to do all you can to prevent theft - Read your insurance policy. It's also in your best interests.
Of course no-one leaves a window open with the intention of assisting a thief. Letting a bit of air in a parked car on a hot day is desirable, but it does increase the security risk - Just ask your insurer.
You can choose to leave windows open and then lie to your insurer (as you advocate) if you wish but I reckon you might wish you closed them if you had a theft. Windows up and alarm on is obviously more secure and also less inviting.
I've now contributed enough to this discussion so that folks can make up their own minds about how they want to leave their unattended cars.