We Jews always remember the bad as well as the good. Many of our holidays, even the most festive ones such as Purim, celebrate times when a great disaster or genocide was narrowly averted.

That said, I don't think in practice Yahrzeit is particularly morbid or that it causes us to dwell on our grief more than anyone else. We get over our losses in time just as anyone does. I don't recall my father becoming overly worked up during yahrzeit for his mother or his father, both of whom died before I was born. It was always just a day to remember and a week to say a special prayer (the mourner's kaddish) in synagogue.

Plenty of Christians say an extra prayer and go put flowers on a loved one's grave onthe anniversary of their death. This is the same thing. In fact, as the original post points out, the name Yahrzeit was first applied to the Christian versions of this practice, then borrowed by Jews to refer to their pre-existing tradition.

Finally, I think it CAN be a healthy thing to recall (not relive or reopen) one's grief. Among other things, it makes one more reluctant to call for anyone else's death. Remembering how it made you feel when Momma died, you may not want anyone else's Momma to die.