Reacting to positive contact elicits it, yes, but only in times of great distress will the cat force its purring. The question then is does the animal purr to comfort itself or is it expressing pleasure in the experience of pain. Is it both? If so, does one assume the animal is not normal and sick in the head? Is our aversion to this "sickness" merely a justified denial at the sight of what could be a form of pure honesty appearing in a natural state?
I would ask the cat myself but I fear its pride would cause it to lie in the face of my query. Perhaps this paradox is desired by the cat. A necessary struggle to prove itself alive. It could be bored with the basic functions of living and desire to create complications in its attitude and actions to force friction, to keep from wasting away into obscure stability. In this way, the animal passes the time distracted with its challenge while continuing to add valuable information to its genetic code which will get carried on through its offspring.
If each successive generation learns better to accept and even appreciate pain, will the species in effect come to defeat pain? Has this already happened? That being the case, the answer must lie in the purr. What is my purr box and how do I activate it, develop it? How long would it take to turn pain into purr? Are they the same? Can I assume my purr has the ability to pain others? I cannot deny the people I have hurt in life. I wonder how much pain I must enjoy before life purrs back at me, to show me the possibilities in my actions.
Oh El! If life is pain than death is found in the purr. Comfort would then lead toward death. Death must truly be the happiest states of being...
Acknowledge the pain, enjoy it even, but don't forget to keep purring for a happy death.