Briefly the Peltzman Effect is that regulations to improve safety may cause unintended greater harm because people now feel safer and thus will take greater risks that could affect others. His classic example is laws requiring people to wear seatbelts did not lower traffic harm but increased it. You feel more invincible with a seatbelt and an airbag, so why pay as much attention as you used to without these devices? Imagine how much harder you'd charge someone in football if you were both wearing helmets than if neither wore one. (Here is an EconTalk podcast with him on the topic.)
But this is not limited to government regulations, as mandatory seatbelts and airbags could have arisen purely through consumer demand, if they were truly that crazy about safety features. The same greater degree of recklessness would follow.
I think we see this in consumption of junk food by children. Here the ones demanding safer food are the parents, all part of the health food craze that began in the 1980s but got crazy over the past 20 years. Surprisingly -- or not -- this matches the timing of the obesity epidemic (and of all other diseases within Metabolic Syndrome, like diabetes). It struck young people somewhat later, beginning around the late '70s and early '80s for adults and by the late '80s to mid-'90s for young people.
The main culprit is the switch away from animal products to a carb-heavy diet, especially loaded up with grains, starches, and sugars. Now where would kids get that kind of food from? Breakfast cereal, which is almost all grains and sugars. This is the time when bacon and fried eggs started vanishing from little kids' breakfasts and were replaced with cereal. Kids eat way more sugar than they did before the late '80s / mid-'90s onset of the youth obesity epidemic, and how much junky cereal parents allow their kids to eat plays a big part.
Back in the '80s, cereal was frank about what it contained -- lots of sugar. (See here and here for a reminder.) Aside from all the cereals whose names had "sugar" in them, there were those with "chocolate," "cocoa," or "chocula," as well as ones that boasted their likeness to candy and dessert -- Reese's Puffs, Rocky Road, Ice Cream Cones, Cookie Crisp, etc. It was often vibrantly multi-colored like candy, sometimes even having brightly colored marshmallows.
No parent can look at those cereals and think, "Gee, the commercial says it's 'part of a complete breakfast,' so why not let Tommy gorge himself on Sugar Smacks?" As the health food foot soldier consumers stormed the supermarket, one of the first aisles that they razed to the ground was the cereals. I remember that aisle stretching into infinity, sometimes spilling over into an adjacent aisle, and with such a wide variety to choose from. Not that I eat processed carbs anymore, but I've checked my local supermarket's cereal aisle from time to time, and 1) there's not as much space devoted to it as before, and 2) nearly all of the candy-and-dessert types of cereals are gone, with so-called healthier alternatives in their place. You know, those 500 variations on granola and primitive cereals like Chex or Frosted Flakes.
When the parent sees Frosted Flakes, Frosted Mini-Wheats, Honey Nut Cheerios, etc., they recognize that there's some sweetness there ("frosted," "honey"), but it doesn't sound so bad. At least it's not called S'Mores and doesn't have marshmallows. Because the new cereals adopted during the health food craze appear less junky, parents will let their kids eat more of them. By contrast, when the cereals that parents bought for their kids were such flagrant sugar bombs, they would think twice about letting their kids pig out on them.
If the new cereals were made out of spinach, then eating more of the stuff wouldn't fatten up the children. But just look at the label and see how much carbs and especially sugars there are. The difference is cosmetic only -- like grade inflation. The advertizing about how natural, organic, bla bla bla it is with its fiber, whole grains, and yadda yadda yadda, is just there to assuage the parents' guilt. "I want to let my kid have some sugar, but don't make me feel bad doing it -- sell me a believable story about how it's somewhat healthy." The unintended consequence of this grade inflation is that kids eat more junk (with inflation, now perceived as not-so-junky), get diabetes, and grow obese.
Before the health food craze, parents used their own judgment about what was obviously harmful food -- they did not demand that the food producers wipe out the candy-like cereals and give them "healthier" alternatives. During that period, there was no grade inflation of junk foods, therefore parents had no illusions about its nutritional quality, limited their kids' consumption, and kept them from getting really wrecked.
It's just an impression, but this seems to apply to sugary junk food in general. Hostess used to sell snack pies with pudding filling but now only sells ones with fruit / syrup filling. Pudding is obviously a dessert, while fruit sounds healthy, so it's OK if my kid eats 150 g of sugar in one sitting. I looked through the cookie section of my supermarket and again found much less of the not-even-trying-to-hide-it sweetness. Like the cereals, the cookie selection looked so boring, the sugar waiting behind a disguise of bland-colored primitive-sounding snacks that boast of having so many grams of fiber or whole grains -- like your kid gives a shit. That's obviously to assuage the parents' guilt, which again causes them let their guard down and allow their kid to eat way too much sugar. Back when most of these snacks had sugar in the form of chocolate, cream, and icing or frosting, parents could tell that their kids shouldn't be eating much of them.
It's like at Starbucks or the Whole Foods bakery section, where shoppers allow themselves to be deceived that their blueberry scone or banana nut muffin isn't simply 5 lbs of sugar and a bit of flour. I mean, it's not like those tacky candy bars that poor people stuff their unsophisticated faces with: it's healthier. Right, that's why the skin is falling off your face and you have a beer belly.
Everyone wants practical dieting advice, especially during the summer. Most people would benefit by just cutting their carbs down to 40-60 g a day, but then most people would not be able to withstand the peer pressure to gorge on grains all day -- "What, do you think you're better than us 'cause we eat bread?" So if you're going to include a larger amount of carbs than you should, you might as well make it more obviously dangerous carby foods. That way you won't lull yourself into a false sense of security and blimp out and get diabetes from eating granola bars, pasta, and fruit juice all day. I don't mean eat a cake instead of bread. I mean, given a certain amount of carbs that you're going to eat, take that amount from a source that's more likely to sound your alarm.