Don't despise others just because they're poor.

Literal

Poor [just-because-だからといって] others [object-を] despise [don't-な].

~からといって is a key pattern meaning 'just because X (doesn't mean Y)' — it challenges the assumption that one thing justifies another. 軽蔑する is a formal word for 'to despise.' するな is the most direct negative imperative.