It seems like most of the comments are missing the point; different types of bike thieves steal different kinds of bikes.
A decent lock (used properly) will stop someone from stealing a bike just for convenience. A cheap/ugly bike will not get stolen by a thief looking for high-value bikes.
Where I live, high-value bikes are being targeted and stolen. A friend recently told me about his office being broken into in the middle of the night; the only thing stolen was a >$5000 e-bike that was locked to a stand, which was bolted to the floor. An angle-grinder and a possibly stolen van where used to facilitate the theft. A very highly targeted theft, which would not have happened to a cheap/ugly bike. On the other end of the spectrum, any bike with a cheap lock, an improperly used lock, or no lock, is highly susceptible to going missing.
Just in the last few weeks, two friends lost bikes that cost about $1000 each to replace. One was locked with a cable (I told him, before he lost his bike) and the other was locked overnight with a folding lock (I don't know the model/quality).
My bike is locked (with a good-quality U-lock through the rear wheel and rear triangle) whenever I'm not sitting on it, but for a bike that's worth >$1000, U-locks do get cut around here. I really don't know of any cheap/ugly bikes that have been stolen, around here, if they're locked up well.
With that in mind, and being comfortable riding a bike that may not be the most aesthetically attractive by contemporary standards, is there "protection" in taking a nice/desirable commuter bike and either (a) making it look like a pile of rusty pipes, or (b) spray-painting over the make/model that's printed on the frame?