While sports and fitness marketing does exist, marketing that go against sports and fitness is just as powerful, if not more powerful: conveniences that encourage people to be physically lazy, wide availability of food contributing to obesity, huge number of non-physical hobbies that may well overshadow physical hobbies in attractiveness. Instead of leaving the next generation to the whims of marketers, I am advocating taking the proactive stance and encourage children to be healthy.

Also, actually trying out various sports is a completely different experience from merely hearing about how good a sport is. Many families don't value fitness enough, and won't encourage their children to try sports. Many other families simply don't have the resources or energy to let their children try one sport after another until they find something they enjoy. But a school is well-equipped to show children dozens of fitness options.

The rest of your arguments aren't related to the appropriateness of having mandatory PE classes, but to the way PE is currently taught at school. I do agree that many - if not most - PE curricula could use a lot of improvement. I also agree that in some countries PE is overvalued to the point of neglecting other subjects. But that's no argument for saying that there shouldn't be mandatory PE; it just means PE classes can use a revamp.

Also, the benefits of exercise are not "nullified" if you don't exercise as often as some people. They are lessened, that's all. Studies are showing that even exercising for a few minutes a week can lower your chances of developing health issues. More exercise than that, and the appropriate types of exercise, will be even more useful.