The main reason that canned tomato soup or other canned soups are considered bad for your health is due to the high amount of sodium that is contained in the canned tomato soup and other canned soups.
Homemade tomato soup is much more healthier for you than canned tomato soup because there's not as much sodium in it.
When you consume too much sodium the sodium can increase your risk of heart disease, heart attacks, strokes etc.
When canned tomato soup or other canned soups are eaten in moderation they are healthy but if you already suffer from heart disease then you should avoid eating too much canned soups including the canned tomato soups.
If you want the healthiest tomato soup or other healthy soup you should make your soup at home so that it doesn't contain a lot of sodium which is bad for your health.