I don't know what it is you can tolerate or even why you think you know what you'd tolerate as a coach, but one thing you can't do is scale the punishment out of proportion with the offense. Selfish penalties are tough to deal with, but the bench for an entire season for one bad mistake is out of proportion and may inhibit some team aggressiveness and physicality. Nobody wants to make a mistake and lose their season.
I hear what you're saying and understand your position. It makes sense.
I'll try to clarify. I can tolerate a roughing the kicker penalty that costs us the game, or roughing the passer, or a late hit, or an out of bounds hit, or an unnecessary holding penalty or jumping offsides for not knowing the count penalty, all of which end up costing us the game. I don't want to inhibit my players from playing aggressively and I wouldn't punish them for a mental football mistake. In my opinion, that all goes with the territory and is part of the game. I would feel for my player in that type of case and know that it was the last thing in the world he intended.
But, if one of my players got into an altercation after the play, or sought revenge, or was "defending" himself or one of his teammates after the play was over, and ended up getting a penalty that cost us the game, I would come down very hard on that player. That's what I, personally, could not tolerate.
But, I would take responsibility to train them on a daily basis to never incur such a costly penalty. Everyday before and after practice, during our evening talk before a game, during my pre-game speech and my half-time talk, I would pose this question to my team: "gentleman, what are you going to do every single time an opponent tries to pick a fight with you, pushes you down after a play is over, makes a dirty hit on you, calls your mother a whore and your grandmother a slut, tells you you're a pussy, calls you a no-good-chicken-sh$t Gopher, tells you your coach is a "freak", drags you by your face mask across the field, mashes your face into the ground underneath the pile, what are you going to do for your team, your coaches, your school and your State"? Then, I would require them to shout "we're going to just walk away Coach".
I realize I'm being a little or a lot goofy here. But knowing that one penalty like this could, however unlikely, cost us a game, which could cost us a championship, which could cost us a certain bowl berth, I would believe it's worth the extra minute or two to do something like this.
I'm guessing there are one or two coaches out there in the country at some level who could look back and tell you how a ridiculous, temper-related and non-playing penalty cost them not only one game, but a championship, or a playoff berth, or an undefeated season, or the chance to play one more game for a group of seniors, or something like that.
Now that I've written this, I realize I'm making too big a deal here, but I'm hoping you get my point.