2. In the second Australian innings, Clarke the Australian Captain also refused to walk. He was given out by the umpire but challenged the decision. Only after being given out by the 3rd umpire using the technology did he walk. I have not seen any vilification of him as as happened to Broad.

Presumably Clarke made the challenge (as allowed by the DRS system) as he believed he was wrongly given out.

Whether one agrees or not with Broad's decision not to walk, I don't think there is any doubt that he knew the umpire was wrong. His challenge to the umpire (to compare with Clarke challenging the umpire) would actually have been to walk.