How would you derive that someone “dislikes jews because they are jews”? Do you listen to them talk and make a decision following your gut? Do you make an MRI image of their brain and measure their brain waves to read their mind?
You would have to work with their past actions. And then it becomes non trivial to define “anti-semite”.
So it is not really about “what does the word mean” but “how do you decide who fits the definition and who doesn’t”. People are concerned about this because it is very hard to make a law that 100% only fits to the people you want to target (leaving asside wether the principle is correct or not).