It's okay. I won't do anything that would be bad for you.
I won't do anything that would be disadvantageous for you. Leave it to me.
I won't do anything that would be disadvantageous for you.
あなたの不利益になるようなことにはしない。
不利益になるようなことをちょっと直訳的にanything that would be disadvantageousにしました。自然に使える表現ですがdisadvantageousは難しかったら
anything that would be bad for youやnot good for youでも問題ないです。
最後にくる「から」という日本語の文法は直訳的にbecauseとかになりますが、
この場合では要らないです。逆にIt's okay because I won't do anything that would be bad for youは少し不自然です。
ご参考になれば幸いです！
「大丈夫。悪いようにはしないから。」
- It's okay. I won't do anything bad.
- It's okay. I won't make it worse.
- Don't worry. I won't do anything to make it worse.
「あなたの不利益になるようなことにはしないから。わたしに任せて。」
- I won't do anything bad to you. Leave it to me.
- I wouldn't do anything bad to you. Trust me.
アメリカ合衆国 
