で判断してはいけない

must not judge by

→ で
phrase Rare #36,593
must not judge by Used to say that someone or something should not be judged based on a particular characteristic, appearance, or other criterion. 判断 means “judge” and で marks the basis or means.
JA: 人を学歴で判断してはいけない。
EN: You must not judge people by their academic background.

人を外見で判断してはいけない

You shouldn't judge people by their appearance.

人を見た目で判断してはいけない

You shouldn't judge people by their appearance.

をもっているもので判断してはいけない

Don't judge people by what they have.

本をその表紙で判断してはいけない

You shouldn't judge a book by its cover.