I rarely ride on the sidewalk. There are spots where this is required by law, eg on certain bridges with high speed roadways, etc. In urban areas, it's very unsafe ... and I have a very intuitive sense of that, so it's very uncomfortable for me. And so I don't do it. But I think the rule here is that people should ride as they see fit, and let others do the same. So if you feel safer on the sidewalk, and aren't causing a danger for others ... it shouldn't matter very much what I think of that.