The only advantage I can see for stalls is that if your stall runs out of toilet paper you can beg the person in the next stall to pass you a roll under the partition.

Ventilation? Why not use fans?

Ease of maintenance? If ease of maintenance instead of user experience were the driving factor in software development, we would all still be using command-line applications exclusively. Shouldn't the "user experience" be the driving factor in bathroom design too?

Safety and security? Even toilet stalls have locks. Does anyone NOT lock their stall while using it?