Judah,
Hope you are not taking any of this personally as although the debate came from your post, we all agree your approach in that game worked. (just in case anyone thinks I'm pointing fingers, which i'm not).
I agree with the try and keep cards in pockets and that they will need to come out if necessary.
I really do find the whole mass brawl with the outcome being a bollocking and a scrum (except for maybe a few incidents where the game has maybe allowed it to be such, never had one though) hard to fathom.
If two players knock ten bells out of each other despite your whistling, they are going to be carded, almost certainly in everyones games. If the teams are doing their best to help you stop it, I can see the reason is telling the capts "Thanks for keeping your players under control, those two are now gone (10 mins or good), we'll go with the sprit of the 28 other players that want to play rugby and have a scrum to x (either team in possession or attacking team if no team in possession).
However,
If you have 15 v 15 who are hitting each other, regardless of your shouts and/or whistle and eventually only stop when they stop (because we all know that we cannot physically stop it). Then how can we really start that with a scrum? How can that be justified in law?
"Captains, you're all as bad as each other so we'll have a scrum to blue!"
That to me doesn't work, there has to be a penalty and almost certainly (not 100% but can't be far off it) has to be cards, and if you can't card the ones who started it, then card a runner in from each team. There you have your equity. Penalty to defence unless you clearly see reason for otherwise, why? Because the defence will almost certainly kick for a line out, game then starts as normal somewhere else and teams can play rugby, if you give it to the attacking team, they may be close enough to run in a try or kick 3 points at goal that may make a big difference. You may say a penalty against one or the other isn't equitable, but it's more equitable than a penalty and points against one team.
Another reason (IMHO) why cards need to be used is that you are then showing the players they won't get away with it.
"Captains, I didn't see what started it but I saw blue 15 come running in from his own half to throw punches and red 14 did the same, these two players will tae no more part in the game and if we have a repeat more players may receive the same sanctions, do we understand? Please take 1 minute to talk to your players we will then restart with a penalty to xxx"
if you just go bollocking scrum the players may still be annoyed/frustrated/angry enough to get the person that just hit them, but if you have already shown two cards, they will have a second thought about it because they know the team will suffer more (not just get a first suffering).
That's my full view on it. Maybe we should have a poll?