My guess is that some people are not comfortable with inequality amongst nations. If that person went to Cuba because it was cheaper it would either mean that: A) the quality of care in Cuba is somehow worst. or B) The quality of care is the same but the U.S. is somehow inefficient. But since it's because of a new drug developed by Cuba's own pharmaceutical industry it shows the prospect of other nations becoming/being equally capable/fortunate, which many support.