I don't think you should keep attacking him/her like that.
You don't have to be so hard on him/her.
Isn't it mean to keep attacking her like that?
英訳１：keepは「続ける」、attackは「攻撃する」なので、「そんな風に彼／彼女を攻め続けるのはよくないと思う」という意味の文になっています。
英訳２：not have to ...は「…する必要はない」、hard on ...は「…につらくあたる」という意味です。
英訳３：このmeanは形容詞の「意地悪な」ということ見抜けましたか？ 動詞のmeanなら、be動詞が使われるはずはありませんよね？
その他の言い方：
- I don't think you need to keep attacking her like that.
- You don't have to keep going at it like that.
*go at it「激しくけんかする」
- Don't you think it's mean to keep going at him so much?
*Don't you think ...?なので、「…と思わない？」というニュアンス。
- Do you have to keep attacking them so much?
- I don't think it's a good idea to constantly attack them that much.
*constantly「絶えず」
- I don't think constantly attacking them so much is the right thing to do.
アメリカ合衆国 
