In the 60's, sack dresses were popular too- but they had a certain modish, a-line structure to them that made them seem fresh and carefully constructed. Sure, they weren't for everybody, but they looked really good on fake-pregnant Mia Farrow in Rosemary's Baby. The dresses today don't have any structure. Most of them just hang from the collar like a smock, looking way more like maternity wear than something poor Rosemary ever wore.
A good example is the "Kate & Kass Dominique Brown Dress" on the upper right. This dress is so horrible I truly cannot bear to look upon it. It's barely a dress. I don't even know what it is, but of course the description on shopintuition.com not only dares to say it was inspire by both Rosemary's Baby and Gloria Steinem (how did it get so trendy to dress like Gloria Steinem when most young women today are totally unversed in feminism? I guess that's a separate issue.) Of course, they also suggest this would look "great with a belt at your waist or hips." Belts are not for creating a waist when the dress you are wearing is shaped like a garbage bag! Whatever you are wearing should have enough shape on its own! Belts are merely for emphasis, or perhaps holding up one's pants!
The frightful thing on the left is also a sack dress, but in a slightly different vein. This Marc by Marc Jacobs "Dee Dee Dots Dress" from shopbop.com has an almost cocoon-like shape. There's an attempt at some sort of structure with the seaming at the top, and then that tapers off, leaving the fabric to huddle around the model's knees, obscuring her figure totally on the way down. These kind of dresses drape in such a way that no matter who wears it, they look like a saggy blob. Plus, is that denim? I mean, it doesn't say it is, but it looks like denim to me. Wearing denim dresses is always a big mistake. This dress is $358, and really makes me long for the days when Marc Jacobs designed cute things.
I know dresses in this shape are hot right now, but they're never flattering if their shape doesn't somehow echo, and in turn, flatter, your own. Besides that, everyone who bought one of these dresses is going to look at photos of themselves in ten years and wonder why they were wearing a smock, and if they were pregnant when the picture was taken.