Jhannes personally asked me a question, "Is happiness a morale obligation?" I do not know how it relates to the Prager hubages article exactly.
I believe the rabbis do say that "Joy is an obligation" or certain sects believe this to be so. To live our lives with joy no matter the circumstances, even through the holocaust, challenges, and tragedies that befall us, that we acknowledge G-d's presence in our lives.
On the flip side, we also have empathy with other's losses.
Truly not an easy goal to fulfill, but one that would lift us out of depression and self-defeating attitudes and mindset.
I don't have a 'how-to' answer, simply a recognition and acceptance of this fact. Blessings to all, with joy and love.