Kerevi's Red Card is definitely a red card.
He rockets into the tackle at considerable speed, and while in isolation there is nothing wrong with this, the degree of danger is higher as the force of impact is higher/ larger and reduces the amount of control he has over the collision. This is pretty obvious watching it both slowly and at full speed. Kerevi's going in too quick for even himself and doesn't have time to adjust to what the ball carriers doing to make a legal tackle. Going hard into contact is clearly high risk and high reward, but ultimately tacklers have an onus on themselves to be in control of their own contact.
He's also upright, and upright doesn't mean 'standing tall' - ball carriers always dip late and brace for contact instinctually, you need to be lower than them.
Then it's direct head on head at the same moment his body hits the ball carriers body, or - there is nothing that will take away from the initial force of the impact.
Easy red - he won't play again on this tour.