It's not that complex really. If smith had competed in the air, he'd have stayed on the field, and we'd all have the contest we wanted. In the end, his challenge was simply poor. The ref applied the rule of law. It kind of sucked, but that's life. Yeah, he could have applied common sense, thought of the bigger picture, but I think many would have cried foul if he had. Particularly if Smith ended up scoring a winning try, for instance. Seen that happen.
Recall watching th BI lions, and the Sonny Bill incident. In my mind I was thinking, well, that's a red, and he should go. That i also wanted an even contest. That this was also a golden chance for the lions to get a victory in the series, they needed. Point is, if SBW had got 10 in the bin, and we had our contest and lost, then I might well have felt aggrieved. In the end, the BI lions played worse with more men, but that's not the issue.
10 minute bin and replacing the offender from the bench seems a good answer, but ultmately, the penalty for the offending side is reduced. I could envision managers, teams or players taking advantage of this change to inflict some real hurt on the opposition, knowing the worst can happen is a 10 minute binning, and a replacement. We'd have a host of dirty late tackles on the hour mark when players are being replaced anyway.
In the end, we all know a player in the air can't be tackled, and if you want to touch him, you have to be seen to compete for the ball. It's pretty simple really.