I agree with several of the other answers here, you need support for the arches. Here in Brazil everyone wears flip flops. I have seen people jogging in flip flops on the road for exercise.
Goodness knows what damage is done. After a day on flip flops my feet ache. I prefer to wear a running shoe.
I do know that flat shoes take the arch away from your foot. At one time I was wearing sneakers all the time and my foot became really flat. Once I started wearing heals again it curved again.
But if you want the most comfortable sneaker ever, get dr. scholls fit sneakers. I have never had a more comfortable sneaker. Plus they have an arch.
Well ideally shoes with arches are the healthiest but I am not entirely sure that is splitting hairs in this case. If you really want a healthy shoe you could go to a shop that make orthopedic products and shell out a couple hundred for a pare of shoes that will make your podiatrist sing. orthopedicshoesforwomen.com.
I think they are. I saw an episode of Dr. Oz where he said flip flops are one of the worst shoes for feet because they have no arch support. I think arch support is necessary.
Flat shoes are definitely bad and unhealthy for feet. I work in a shoe store and a ton of people who have worn flat shoes comment on how they hurt their feet and give them back and joint pain. You want a shoe that has arch support.
A running/athletic shoe generally has the best arch support but it depends on what you are buying. You also need to know what arch type you are whether it be flat, medium, or high. One thing you can do though is put insoles into your flat shoes to make them a little healthier.
Just replace the insole in the shoe with a dr. scholls or a spenco insert. The ones with the gel don't give very good arch support and they don't last very long. They are mainly for comfort.