Popcorn is bad for you due to the high calories, high fat and high salt content as well as artificial additives and potentially harmful chemicals that is added to commercially prepared popcorn including movie theater popcorn.
Plain air popped popcorn is not as bad for you as long as you don't add additional salt or butter or seasonings.
When eating plain popcorn the plain popcorn is a pretty health snack.
Most pre made flavored popcorn and movie theater popcorn can be extremely high in saturated fat and calories which can contribute to weight gain and increase in your risk of heart disease.
Large portions of popcorn, especially the popcorn made in movie theaters can contain a high amount of salt and sodium which can cause high blood pressure and water retention.
And some popcorn is often prepared with artificial flavors, unhealthy oils and additives such as diacetyl, which has been linked to respiratory issues such as popcorn lung.
Even pre packaged and microwave popcorn bags can contain chemicals such as PFOA which is a likely carcinogen and diacetyl, which can pose some health risks when heated up.
Although plain popcorn is a good source of fiber, eating excessive amounts of popcorn including salted and buttered popcorn can lead to bloating, gas and constipation, especially for people who are not accustomed to high fiber diets.
The texture as well as the taste of popcorn can also make it easy for you to overeat, and lead to a higher intake of calories and potentially contribute to weight gain.