I've never been comfortable with heel hooks, the same way I've never been comfortable with certain spine attacks or neck cranks.
The certain spine attacks and neckcranks (note: not all) should need no explanation. Anything that can seperate certain vertabrae and cause paralysis has been mostly banned from sanctioned MMA, I believe.
Heelhooks in my opinion are way, way more dangerous then ankle locks, kneebars, calf crushes etc.
There's an easy argument that probably will be made: Don't get caught. Easier said then done. Silva is a legit blackbelt in BJJ, he got caught (maybe through a bad judgment), and his career could be over. The moment I saw him tap I knew what had happened.
Shogun Rua's career is in jeopardy, not from a heelhook, but from the same ligaments in the knee being damaged that a heelhook would tear.
I believe with a fighter as dangerous and skilled as Imanari, using heelhooks defeats the point of having a tap out. A tap out is there as a sign of submission before any serious damage takes place. It's conceding checkmate. A tap out is no good if you're tapping after your knee is completely fucked, and a heelhook does not give a fighter the same period of grace as other submissions do.
Continued use of heelhooks will only serve to retire fighters too soon, and possibly spend the rest of their life using a walking stick.
I personally would have no problem seeing heelhooks removed from the sport for that reason. A technique used to permanently disable an enemy on the battlefield in feudal japan has no place in today's MMA, in my humble opinion.