This, to put it mildly, is fucking terrifying. I haven't been body-checked to the ground yet, but I've seen some videos of it, and in my not-expert medical opinion, it seems to be a much more dangerous maneuver than rolling through a vacant intersection. As the video above shows, the Idaho stop is a beneficial move because it allows you to conserve energy by conserving momentum, which is sort of obvious. More surprising, though, is the fact that Idaho (which employs the law that colloquially bears its name) has a very solid bike safety record. When properly deployed, it's a totally safe behavior.
"Don't break the law and you won't get in trouble." That's the counterargument, right? Well, as demonstrated above (not to mention the recent local and national stories of unwarranted police violence), that doesn't always work. You might still get tackled, or worse.