"...They kill...knees and shoulders don't....as far I know.
Or, how about a campaign against inhuman treatment of workers?...Or cruelty against animals? They can start at Souk Waqif...."

There are people fighting for different issues, everything goes in parallel. Also the level of importance which a person gives to different things differs based upon the his ethics and principles.

So for you displaying of knees and shoulders may be a small or insignificant issue but for muslims it is not a small/minor issue as it is related to modesty of women and the negative effect that immodest dressing has and the far reaching consequences it has on the society as a whole.