The actual rights and wrongs of the settlement of the Palestine mandate are irrelevant, and only lead to useless finger pointing. Plenty of pro-Palestinian Americans and Europeans like to point the finger at Zionism, claiming that Palestinians had every right to resist people who were kicking them out of their land, but never forget why or how those Jews ended up there.
The centuries of persecution in Europe didn't do it. Hell, even the Holocaust didn't do it. What turned Zionism from a fringe movement into a mass movement was the decision taken by the Europeans, Soviets and Americans to deny surviving and displaced Jews the right to return home. Most properties owned by Jews prior to the war had been taken over by Europeans, and most European governments preferred not to try and change that situation. As a result, many European communities actively resisted the return of Jews, and there were several instances across Europe where Jews who had survived the Nazi regime returned to their homes (and remember, these were their homes), they were attacked and in some cases lynched and murdered by the local population.
Now, quite naturally, after a decade of the unspeakable under the Nazis (and Soviets), with European civilians actively resisting their return, and most international governments closing their doors to further European immigration, many tried to emigrate to Palestine. For most, it was quite simply the only option. When they did, they were often intercepted by the British and sent to internment camps on coast of Europe. Many of these were survivors of death camps, and as you can imagine, such a post-war existence did not seem like 'liberation' to them. These camps were quite literally breeding grounds for Zionism, and many of the immigrants changed from default Zionists to militant activists, prepared to fight and die when they reached Palestine.
So decades later, when entitled Europeans and Americans who have lived through 'optional war' or even total peace try to lecture Israelis about how they never had a right to be there in the first place, it doesn't go down terribly well. Our governments created Israel, and Europeans and Americans are totally responsible for the situation that now exists. It is totally unfair to then blame Israelis for being there in the first place.