I understand there is a chance for those who carry the trait to have iron overload if they take iron supplements. Is this true?

Well, people who were diagnosed with Thalassemia are prone to get iron overload even without consuming iron supplement or blood transfusion. Patients were having ineffective red blood cells production which can lead to overabsorption of iron from the intestine. This is caused by some kind of misinterpretation by the body thinking that the anaemia was caused by iron depletion when in fact the iron level was normal.

Optimal medical care should be based on the optimal outcome, not on a patient's ability to pay.

Well, I agree but you should know that there are many factors which can contribute to the outcome of a treatment and one of them would be financial instability. Let say the price of the drugs were 500 USD per month and the patient salary is 1000 USD per month. He/she (the patient) would have other things to pay for (school fee, bills, rent) which if we add up with the cost of the medication can total up to more than 1000 USD per month. What do you think the patient would do? He might want to skip buying the medication until he has enough money to buy for another month supply.

This is an example of how financial instability affects compliance. Can that action be considered as an optimal health care? Nope. That's why it is important to consider the socioeconomic background of a patient before deciding on treatment modalities. In medicine, we are not only treating the disease but the patient as a whole (holistic approach). It will be unrealistic to treat patients with the most expensive kind of drug while leaving them with thousands of dollar of debt.

It's tough but as long as there is an alternative, it should be fine. The field of medicine is advancing day by day.