As noted in Mountains Beyond Mountains, there is significant global inequality in access to healthcare, and this is closely tied to the economic inequality that occurs globally. This unequal distribution of wealth and healthcare occurs because of our systems of trade and economics. Free trade and capitalism, the currently dominant global ideologies in these areas, are both primarily focused on increasing the efficiency of production through innovation. These ideologies do not try to ensure that everyone has equal access to the increases in efficiency. Thus, it has typically fallen on governments and nonprofits to ensure widespread access to these innovations. However, this access typically comes with higher taxation rates or requires significant charitable giving. In both of these cases, this money could alternatively be directed toward developing further innovations. This leads to a trade-off. With wider access, innovation can become slower, and vice versa.
The question for society then becomes, At what point is the loss of innovation worth the increase in access? In the case of healthcare or food production where human life is at stake, I would say that ensuring wider access is worthwhile. Therefore, I would personally tend to agree with Paul Farmer.
However, this is a simplified version of the moral dilemma associated with inequality. Additional complications come into play in the real world. For example, increased inequality has been associated with societal instability. In some cases, this has led to widespread protests, violence, or even revolution. On a personal level, this again leads me to support reducing income inequality.
The Gini coefficient is a measure of inequality. The World Bank page linked below shows it for different countries. A higher coefficient suggests increased inequality.
The resource from Columbia, also linked below, discusses inequality and the social costs associated with it.