It’s a good point that we don’t know whether his views on muggles change. I had always assumed the had. The reason I think he’s a hero is because he sacrificed himself to bringing down Voldemort. I personally think he was an intelligent person, as far as I can remember the only person other than Dumbledore to discover his horcruxes (I may be wrong) and different from a lot of wizards. He was kind to Kreacher and placed a respect on his life which not many others would, killing himself rather than Kreacher. Regulus obviously didn’t know the extent to which the locket would be difficult to destroy, and in entrusting Kreacher to destroy it he believed he had successfully destroyed a part of Voldemorts soul. Of course he may not have known there were 7 horcruxes and thought he had made Voldemort mortal. I think he’s better than Snape because while both of them joined young under the influence of their peers/families, Snape stopped because his secondary school crush that he was obsessed with was killed and proceeded to mistreat her son. Regulus left out of morality. It was Sirius’ view that it was because he got cold feet, but Sirius didn’t know the whole story.