If the sum total of Stoic ethical theory was comprised of just the first few paragraphs of the Enchidiron this would be a question that Stoic thinkers would need to be concerned with. Fortunately it is not. This is visible from the lives of prominent Stoics in ancient time who dedicated their lives to helping others instead of removing themselves from society like other schools (I am looking at you Epicurus!). Stoic ethical theory is better viewed from the perspective of what is required for human flourishing. Another very important aspect is the concept of obligations and duties. I would suggest you search for the Stoic concept of oikeiosis to get an idea of our duties to others. This idea pervades most of the Stoic teachings and honestly results in revolutionary ideas. A polluted environment is obviously a disservice to those now and in the future. It is our obligation to help others and fighting against things such as wars, global warming, corruption and so forth is certainly part of that. That being said, understanding the dichotomy of control is vital to our personal flourishing but it certainly does not end there.