My dad looked at several franchises over the years and despite going pretty far down the road with one of them, never pulled the trigger on opening any of them.
I deal with franchise owners from time to time and these are the major issues I see:
Corporate can screw you at any given time. Get a bad or greedy group of executives or board members and they will milk the franchises dry by increasing fees, costs of materials, ect.
There is a reason they make you sign a confidentiality agreement.
Corporate usually has a few "flagship" franchisees that they like to parade around in order to sell more franchises. These individuals typically do very well, and may even get special treatment when it comes to territory etc. to keep them promoting the franchise.
Bad press at any location is bad press for you.
Lack of diversification.
If it was really that good, they would be opening corporate stores vs franchise locations. What they get with a franchise is a vested manager (you). If you step out of the picture and try to hire someone (or several people) to run the location for "passive income" the probability for success drops significantly.
There are certainly people that have built up tremendous incomes with franchises, but they typically do it the old fashioned way, reinvesting the profits over and over, plus a bit (or a lot) of leverage that they are lucky enough not to have come back and bite them. For the reasons above I don't think I would ever be too interested in a franchise. But if I was, an existing location with good performance records would be preferred, unfortunately these usually come with a price tag to match.