His rhetoric was so militant that he literally inspired Jews to become terrorists in several instance (such as the JDL and Baruch Goldstein), not an easy thing to do to our morally-sensitive people. How this be good? The proof is in the pudding.
As R’ Hirsch, Rav Kook and others have written, Jewish nationalism should not be like non-Jewish militant nationalism (“vainglorious nationalism” as R’ Hirsch is translated), about puffing yourself up and putting others down, as a justification for injustice and war. But that’s what Kahanism is.
We can ultimately achieve more or less the same thing (incorporate the territories into Israel (a one-state solution) while maintaining a comfortable Jewish majority) though more moderate, compassionate rhetoric and means. If Jewish Home (in its current fairly moderate version) or the right-wing of Likud were to get in power, I believe that is what they would do.
There are religious settlers who believe strongly in what they are doing, yet who get along well with the local Arabs and strive to live in peace with them and use gentle language in pacifying them and improving their lives practically. That, plus getting rid of the terrorists and stopping the pro-terror incitement within Arab society, will work better than far-right nationalist grandstanding.