High-mindedness is the noun: the quality of having very high moral standards. You might praise a leader’s high-mindedness, or you might doubt it — “all that high-mindedness, and then they took the money.” It names the whole stance, not one good deed. The word is formal; in everyday talk people are more likely to say “she has such high principles” or, if they are less kind, “she thinks she is better than us.” From high-minded + -ness, in the ordinary way English builds a quality-noun.