It is possible to rationally prioritise between causes without engaging deeply on philosophical issues
From the top of my mind, I'd say that it depends what counts as "philosophical issues". Typically, whether we consider animal welfare a priority raises philosophical issues, because the moral value of animal suffering is a matter of ethics—and, consequently , of philosophy. Same thing with environmental or population ethics, and so on.
However, to a certain extent, some causes can be compared without raising philosophical questions—if we can compare them with a single set a criteria (such as QALY, and so on).
From the top of my mind, I'd say that it depends what counts as "philosophical issues". Typically, whether we consider animal welfare a priority raises philosophical issues, because the moral value of animal suffering is a matter of ethics—and, consequently , of philosophy. Same thing with environmental or population ethics, and so on.
However, to a certain extent, some causes can be compared without raising philosophical questions—if we can compare them with a single set a criteria (such as QALY, and so on).