With Kagan and Sotomayor, the stakes were relatively low. Kagan was arguably more conservative than the justice she was replacing, which was the best realistic hope for the conservatives, so why would they get upset? Sotomayor was probably more liberal than Souter, but not hugely so. On the most controversial issues, like abortion, they were expected to vote the same way. He'd long been a member of the four-judge minority on most split decisions, so having her replace him mostly just preserved that status quo. By comparison, Kavanaugh is a hard-right judge being offered to replace a center-right judge who provided the swing vote on a number of critical issues, like abortion. When it goes through, it will profoundly alter the balance of the court and result in a long-standing precedents being overturned. Understandably, for people who don't want to see the court turn a drastic rightward turn, this is a big deal. If nothing else, it's widely expected to end Roe v. Wade, leading to a future when women who choose to end unwanted pregnancies are treated like criminals. The stakes are higher for this appointment than for any going back decades.