You're like many people...you don't understand why God gave us a will, a body, and an intellect:  To harmonize all toward a more perfect expression of our yes to God's will.  You've concluded that we're largely just our appetites and passions.

I'd explain all this to some Catholic who is truly curious about what this all means for us day to day. 

Medical treatment within prudent measures is definitely in line with God's will; it allows others to use their intellect and will and body to serve others, in an ever more perfect manner. 

The number of Catholic inkhorns around here is truly stunning.