With respect, I think it naive to assume that rural France - or anywhere else for that matter - is devoid of petty criminals. Leave your loaded bike locked up in public places and in plain sight and you are taking a risk. It's all about minimizing that risk. In the past, I've employed various tactics to reduce risk when touring in said rural France, like:
* If planning to visit a museum or church, say, while in the town where I've overnighted, I might consider visiting while my bike is still safely locked up where I stayed (having checked first with the host)
* If visiting midday, see if you can spot anywhere you can shut the bikes away, out of sight, while you visit - many French town houses have court-yards. Invest in a coffee or two in a suitable nearby cafe and get chatting

* If you must leave the bikes locked up, make sure they're in a busy place with lots of onlookers and consider covering them with a tied down tarp.
* always take the high-value, highly portable stuff with you (obs.). Ideally you might take
all the luggage with you but that commits you to a) finding a safe place for it or b) lugging it around all morning... Attach the stay-on-the-bike luggage with a cable lock. No deterrance
at all to a pro, but will put off the grab-and-run type.
* minimise the risk by returning to the bikes as soon as you can. Insurance is unlikely to be much help - who's going to pay out when it's revealed that you left items unattended and in public view?
On the day, you'll find yourself doing exactly what you're anxious about and will come back every time to find both bikes and all your gear still there...
