What's supposed to be embarassing about it?
Does Kucherov have the advantage of multiple camera angles, reviews and slo-mo? No, he doesn't. All he has is what he witnessed. If that hit looked dirty from his point of view, or he thinks he needs to respond to show that the team won't be intimidated, then that is all the justification that is necessary for him to react. Going after another player is a spur of the moment decision based on emotions, not the result of a careful decision-making process which included pondering all the evidence to come up with an appropriate reaction (which is why all that wining by some people about the instigator is so asinine, it has never stopped anyone from jumping an opponent, players don't think in that moment, they react on instinct).
Now, Geekie's action were completely unnecessary, at that point Kucherov had already given an answer, and Geekie must have known about what actually happened, but that's why he got the appropriate punishment for it. Certainly excessive, but then again, it is equally excessive to make an opening post like that, which is just as over the top as Geekie's reaction was. It's preseason, and a rookie tried to impress his teammates by showing he would stick up for them. Hardly something to lose much thought over.
Players jumping an opponent after a clean hit is not new, it has happened for decades. For one, because players don't get to see the whole picture, and a hit may looked dirty from their point of view. Secondly, because no one wants to look weak. Someone lays a big hit on your star, you show a reaction, whether it was clean or not. You do not want to let the other team think they can target your best players with big hits. It is obviously okay by the rules, but this isn't about the rules, it is about showing the other team that they will get a response if they do try things like that. It is an intimidation tactic. It is unlikely to prevent anything, but teams will feel better if they respond, it helps with team-bonding, it shows they will stick up for each other and have each others back.
Hockey is played by humans, not by robots. The rules define what is legal and what is not. And while this hit was certainly legal, it doesn't mean that showing a reaction to it is outside the norm. Teams have reacted to clean hits in the past, and they will continue to react to clean hits in the future, because there is more at stake than judging whether something was fine according to the rules or not.