They claim to have the (intellectual) high ground in this debate. [=they claim to have the (intellectually) better position]他们声称在这场辩论中（在理论上）占上风。

These countries lost/ceded the moral high ground [=they stopped being morally better than others; they lost the right to consider themselves morally better than others] when they entered the war to protect their economic interests.当这些国家为保护自身经济利益而参战时，他们就丧失了道义上的制高点。

She believes she has the moral high ground on this issue. [=she believes her position on the issue is the morally correct one]她认为在这个问题上她占有道德上的优势。