Not meaningless, just depends what meaning you get. Say you wanted to filter to "habitable" square milage? You might filter out bodies of water, mountains, areas that get almost no rain, etc.

It is only arbitrary if you aren't intentional with filtering.

I don't agree with the premise of this question.

Anti-semitism IS a brand racism. Your question assumes that some racism is more okay than others. No brand of racism should be more acceptable than another brand. Race is not just color of skin. That is a common misconception though.

If you are asking why anti-semitism is frowned upon, it is because they have been killed, enslaved, exterminated, oppressed, etc. at scale for centuries. There are fewer than 15 million Jewish people alive today.