Personally I have never had any problem with fasted cardio, though I don't do it often. I tend to run later in the day after the weight training. I would recommend taking some BCAA's or half a protein shake before your cardio if you do prefer fasted cardio, for reasons MVP mentioned above, to just preserve muscle.
I agree if your simply looking to lose bodyfat, let your diet do most of the work. Though the added cardio will let you be a little more loose with it. To me, my body responds better when I add in cardio and I'm also allowing myself to be in better cardiovascular shape along with building strength/muscle.
I follow two general rules: Never ever do any serious cardio before weights and if your doing any sort of sprinting/HIIT/Sports, dont do that on an empty stomach.