Of course, sometimes a big singalong of a favorite tune can fall flat. On Wednesday, the movie star Gal Gadot posted her own Instagram video, a montage of celebrities taking turns crooning John Lennon’s “Imagine.” It was a “We Are the World” for the age of quarantine, or a kind of parody thereof: a ragtag chorus of famous people with dubious musical pitch, singing, after a fashion, into their cellphone cameras. The thing is obviously well-intentioned, but the optics are hard to take. In the midst of a global public health catastrophe that is crashing the economy and underscoring gross inequities, images of wealthy actors and musicians warbling utopian lyrics from the comfort of capacious homes and luxuriant gardens — let’s just say it fails to strike the right note.