See appeasement before WW2 for what happens when you let a completely insane and unreasonable dictator get away with ever increasing acts of aggression because you fear the ultimate act of aggression. It never works and it never will. These people ALWAYS look at these situations as proof that ever increasing levels of aggression work. Remember we have already appeased Putin multiple times and let him get away with literal murder. Rigging the elections in Russia, the invasion of Georgia, the assassination of Litvinenko, the attempted assassination of Skripal (one using nuclear material, the other using a deadly nerve agent),f the actions in Syria, the political interference in Ukraine to move it away from the west and the EU, the annexation of Crimea, the multi-year military campaign in the breakaway regions of Ukraine and now full blown war and attempted annexation of Ukraine and sabotaging of international infrastructure.
Did appeasement do anything to prevent him from escalating before? No. It will do nothing to prevent him trying again now. You know what the next step of escalation is? Seeing if NATO is prepared for a nuclear war when Russia invades the Baltics. Would you agree we go all out then or would you let him take them? How about when he invades Finland? An EU state? Where do you draw the line because, unless he dies, he WILL escalate again. We could have done more to stamp this out earlier in the escalations when he could have backed down without losing too much face but we didn't and now it's got to a point where the stakes are high. If we back down again, those stakes will only be even higher next time. With Putin's time likely limited now and his desire to leave a "legacy", that next escalation could occur very soon after we back down. He would love nothing more than to go down in history as the Russian who beat down NATO.