No, flip flops are not bad for your feet. I am sure you are all relieved to hear that!
If someone develops pain and discomfort when wearing flip flops it is most often because the feet are used to being supported all the time in shoes and socks with some heel height and then suddenly going to flip flops that have no heel and zero support. This is not the fault of the shoe it’s a sudden-change that is the issue, if you take the time to strengthen your feet by wearing the flip flops around the house for a few hours every day before it gets warm you will have a lot less issues.
Enjoy the Summer everyone! And enjoy your Flip Flops!