Especially if there are wild animals roaming around. But they also risk getting hit by cars, getting stolen as bait animals, and getting in catfights. Indoor cats average a lifespan of 15-17 years, where outdoor cats average around 5. Most the dangers happen at night though so it may be ok letting them out in the day and bringing them in at night. Or if you have a yard, you can build an enclosure they can see everything through and be outside, while not being able to actually leave the yard. Something like these. Some are bigger or fancier, but there's also smaller ones that can attach outside your window. Or similar can be built DIY. http://comfydwelling.com/outdoor-decor/51-outdoor-cat-enclosures-your-cat-will-love.html