For example, there maybe those who dislike Israel and even want war. But to then say "all Jews are evil" is incorrect. Most don't even live there to control policy. Of those that do, many object to policy. It's like saying some terrorists are Muslim so all Muslims are evil. Or that North Korea is dangerous therefore all Koreans are dangerous. Or America does some bad things therefore all Americans should die. It's all obviously incorrect.
You can have a reason to want to fight a _country_ but there can never be a reason to annihilate a complex, nuanced group because of their skin color or religion etc. There can be reasons for war (which is bad enough) but there can never be reasons for genocide. Americans might have reason to hate Japan after Pearl Harbor but to lock up all Japanese inside the country is obviously wrong.
More generally, there can be very good reason to stop a group organized around an action (eg Neo-Nazis). But to say "all whites must die" (because all Neo-Nazis are white) is obviously an incorrect expansion.
Unfortunately, it's a common blurring that exploitative leaders take advantage of. Today some Western leaders foment hate against all Muslims and some Islamic leaders foment hate against all Jews. In the past it was other groups. It is these leaders that are the danger.
Where is the thresh hold the judgment is made at and will we consistently apply it to all groups? I can think of examples of groups that are reviled by most, yet who have members who don't desire directly evil policies. Some desire forms of what may qualify as oppression that are even seen by the majority as acceptable when you swap out certain groups.
To someone like me, who believes quite intuitively that humans are generally the same everywhere, it's hard to grasp, but I don't see how I can prove it's objectively wrong.