If humans were able to fly there would be many problems. One of them is the fact that people would bump into each other. Another one is that people would trespass very easily.
Immortality is a very interesting concept. However there are many downsides to it. One of the is the fact that you wouldn't die from disease. People would suffer forever if a cure is not found.
Super strength is something everyone has dreamed about. However, it has many downsides. If everyone had super strength, nobody could perform surgery and everyone would die.