By modern standards, and under the current interpretation of the laws the red card should have been shown to Herrera. But I think we go a bit over the top with this "Send him off. ref" mantra.
Was Joe Allen really hurt..? Is he fighting for his life in an oxygen tent right now..? Nah. At worst, he got a few stud marks down his leg. They'll hurt in the morning but he's a big brave soldier. He'll live.
My dad used to get studs raked down his back every time he, very naughtily, killed the ball by lying over it in the ruck, playing rugby for Blackheath years ago. He used to laugh the cuts, bruises and lacerations off, saying "They're not scars. They're medals". Wounds received in action (REALLY taking one for the team) and stoically borne. Football used to produce big men like that too. But not any more.
Yes, I know, players have to be protected or none of the insurance companies will cover them. I know the game has to protect high value players from injury or their agents will kick up a fuss. But a sense of proportion, please.
Allen was fouled. The tackle was bad and merited a red card under the current interpretation of the law. But I think the current interpretation is part of the problem. It has created a climate of hysteria over anything that might inflict anything remotely resembling a bruise on a player. God forbid anybody should actually ever be really hurt..!!
Perhaps one day football will become a physical contact game again. But I'm not holding my breath.