i am not saying its a good thing. i personally hate that too. but i just want to clarify cuz you seem to think china is the only place with that problem. if not then there is no issues.
The main issue with scooters driving on the sidewalk is attitude. They drive as if it is their godgiven right to drive there and every other person (especially the pedestrian, for whom the sidewalk was designed) should get out of their way and if not, i'll blare my horn or push myself through.
As Ariannef said, on some roads scooters have no choice but taking the sidewalk and pedestrians will understand that. However, a lot depends on attitude and Chinese motorists just seem to have an utterly crappy traffic behaviour. And it's not just scooters, it's the general Shanghai motorist attitude.
Much worse than almost any other place i've been, maybe except for Manila (and that's based on experience of having been or having worked in >60 countries. India/Pakistan/Bangladesh are not included, i haven't been there).
5000 years and counting...steep learning curve isn't it?