tar someone with the same brush
US /tɑr ˈsʌm.wʌn wɪð ðə seɪm brʌʃ/
UK /tɑr ˈsʌm.wʌn wɪð ðə seɪm brʌʃ/

1.
同じように扱う, 同類と見なす
to unfairly criticize someone by associating them with a group that is disliked or has a bad reputation, even if they do not deserve it
:
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It's unfair to tar all politicians with the same brush; some are genuinely trying to make a difference.
すべての政治家を同じように扱うのは不公平だ。中には本当に変化をもたらそうとしている人もいる。
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Just because a few students cheated doesn't mean you should tar the whole class with the same brush.
数人の生徒がカンニングしたからといって、クラス全体を同じように扱うべきではない。