Regarding Israel and Hamas, the problem stems from the fact that Palestinians had their property stolen from them, they held title to it, in the creation of the state of Israel and that continued with the terrorists called "settlers". Hamas is a direct outcome of that theft. Of course, it also is a direct outcome of European Christians persecuting Jews since Rome became a Christian empire. Europe failed the Jews and the Palestinians. You brought it up.

That said, people have the freedom to fight injustice with a boycott. Whether that does any good when the ultimate grievances are never discussed and thus the solutions are avoided is another issue.