Why may some see Henry Drummond as a hero of inherit the wind?

He stood up to a whole town and ideology.

Drummond's strongest showing in the courtroom stems from desperation, when the court disallows any testimony on evolution and calls Brady as an expert on the Bible. Drummond's belief in the sanctity of ideas and freedom of thought, as well as his knowledge of Brady's weaknesses, allows him to successfully defend Cates' for speaking his thoughts allowed. In the end, he is an atheist who believes in God, as Hornbeck calls him, because of his respect for Brady's convictions and ideals.

Explain how he stood up to a whole town and ideology.

He was a lawyer who went into an ultra religious town and argued about the sanctity of science and evolution. This is a town that took Scripture at face value. Evolution was considered blasphemy so you can imagine the guy had his work cut out for him.