Translation

有害な / 破滅的な / 害を及ぼす

Meaning

Baneful means causing serious harm, ruin, or destructive influence. It is formal or literary, often used for habits, policies, beliefs, or forces that damage people over time. The trap is confusing it with baleful, which often means threatening-looking or ominous.

Examples

• その政策は小さな農家に有害な影響を与えました。
  The policy had a baneful effect on small farmers.
• 恐怖に基づく教育は子どもに破壊的な影響を与えることがあります。
  Fear-based teaching can have a baneful influence on children.