OK, for so so long so many here have declared this as a No No. Well folks... I think your reasoning is full of poop. ("motorists won't look for you on the sidewalk") Got news for you... motorists won't look for you ANYWHERE. Oh they might see you out in traffic, in front of them, but there is NO guarantee, NO 100% sure way to know that you actually register as "something" to their feeble minds.
So the solution... oh yeah, get a mirror. Right, so you can "dodge" the idiots.
So you are 100 percent in charge of not only not being seen, but for watching out for those that don't see you. Hey, guess what, it works the same way when you use a sidepath/sidewalk. You are 100% in charge of seeing them... only the big difference... it is harder for them to run you over when they have to cross curbs, grassy knolls, telephone poles and maybe even a parked car or two.
Now please understand I am not saying this out of ignorance or lack of experience or skill... I bike commuted in So Cal, on the road, as part of traffic, for well over 35 years... often I was flat out "invisible." This, in spite of bright clothing, flashy lights and lane positioning. I called it "Casper Mode," as just like Casper the ghost, the only folks that could see me were the rare ones that believed in cycling and really looked. Otherwise, I could go right in front of a car, which is stopped at a red light, and see the GASP on a motorist's face as they suddenly realized there was a human in front of them and they could NOT make a right on that red. I saw this and similar situations on a weekly basis. On top of having to be 360 degrees situationally aware, I also had to avoid the "roads are for cars" mentality.
Well, 35+ years of this and I somewhat retired... and left work, and took to paths. BTW I am not really any good "off road..." but that is neither here nor there.
I am now doing a semi-retired (fill the nestegg) contract stint in the "kill the cyclist" state of Florida... and, I am biking. Where I am right now, there are loads of paths and wide sidewalks... and I got news for you... between the driveways, and the street corners... I get a second or two of relaxing cycling. And in the often occurring case where said path is uninterrupted for a long distance... I am NOT constantly staring at a mirror looking for "distracted idiots" about to run me over.... I am riding a bike and enjoying the heck out of it.
Folks, there is a strong case for sidepath/sidewalk riding. Sure, it doesn't work everywhere... like in a dense downtown environment where there are driveways and cross streets that occur every 100 feet. (God help the bike messenger...) But it does work in some places... and it can be vastly more relaxing than the best situation of "bike lane" (oh paint will save you...) or "act and be treated like the driver of a vehicle..." (which rarely included being treated like an equal)
BTW I have been cycling to school and/or work since I was 9 years old... I am now 64... I know of what I speak. I have also taken both Road 1 and Road 2 cycling classes and have had copious training driving both motorcycle and car. So please don't dismiss this as "well, you don't know what you're doing..."
I just want to share this and dispel the myth that one should "never ride on a sidewalk/sidepath."