I know the benifits of being physically fit but what is an argument to not be?

Any help would do, trying to write an argumentation essay on why and why not to being physical fit.

Have you wrote any of it yet?

just the benifits

You can upload it if you want me to take a look at it.

If you need a section on why not to be physically fit maybe you could write about some of the following:
1) Being physically fit requires time, discipline, and dedication. It is much easier to simply not exercise. Not exercising also frees up time for you to do work or other hobbies you might enjoy.

2) Studies have shown that fat people can survive for large amounts of time on their fat alone. In case of food insecurity, fat people would be far better off that their fitter counterparts.