To add to the chorus...
"Nikkyo should not hurt" is different than "pain is not the goal of nikkyo".
With nikyo my goal is generally a structural control. Like most things we do. Sometimes it hurts. Sometimes I might even want it to hurt to emphasize a point (Peter R's inner sadist). It just depends on a larger context that is itself rather resistant to absolute and simplistic discussion on-line (and I don't mean that to sound dismissive, simply that it "ain't so simple"). Shrug.