How can it be ok to use a shoulder charge fairly below the neck, but 6 inches higher is a red card? That then depends on the height of the player being tackled: so if he's short, or is dipping into the tackle, or being tackled and going down, what could have been a fair challenge becomes a sending-off. Too tight to call, and open to too much 'opinion'.

Exactly the same rule as for an arm tackle. When was the last time someone was penalised for a swinging arm to the chest?

There is an argument for that, but personally I believe that they should use the best evidence available to them.

Exactly spot on! it makes the tackler to make sure he uses the correct method. I know it will sometimes be mistimed but the responsibility is on the tackler.