Okay, so Kahanism is a political belief named after Rabbi Meir Kahane who was an American-Israeli Rabbi who lived a few years ago. Kahanism believes in the idea that Jewish people should have their own country, and that all Arabs and Muslims should leave that country, or else be expelled forcefully. Essentially, it means that people who are not Jewish should not be allowed to live in Israel. This idea is called "Jewish nationalism".
Now, because this idea is pretty extreme, it has led to a lot of controversy and criticism. Many people believe that it is unfair to non-Jewish people and that it promotes hatred and intolerance towards other religions and cultures.
One of the reasons Kahanism is particularly unpopular in Israel is that it is seen as a threat to the country's democracy. In a democracy, everyone has the right to their own beliefs and to express them freely. But Kahanism's beliefs are based on the idea that only one group of people (Jewish people) should have control over the country, which goes against the principles of democracy.
In short, Kahanism is a political belief that supports Jewish nationalism and the removal of non-Jewish people from Israel. It is quite controversial because it promotes intolerance and goes against the principles of democracy.