Ok, now that we have a separate topic for this, and thanks for doing that, I will talk about it. If I owned the store, I would, for obvious reasons, find it wrong and troubling, as I would be losing money on an item that I could/should have sold at retail. Myself, or my employees, though, should be doing their due diligence when they "face"(this was what we called moving product to the front of the rack when I worked in a grocery store in high school so that it looks good) the store and move out of place items back where they should be. People get away with hiding things if the store isn't keeping their products tidy.
On the shopper end of it, I can see why people do it, especially kids. Maybe the kid doesn't get his allowance for another week and wants an item, so he hides it until he can get it next week. No real harm done there. The store gets its sale, the kid gets his toy. Did he keep another kid from getting it? Yeah, but there is no real crime committed, so I don't get too worked up about it. As for adults, it's going to be done in the name of money, and this is where the lines blur. I doubt Joe investor is hiding a set so that he can buy it next week for his son/daughter. He is hiding it so that he can come back at sale time and get the item for less than he would have normally paid for it, and this becomes a moral issue. It's not outright stealing, you're still paying for it, but if it was an item worth hiding, the store was going to be able to sell it for a higher price.
In the end, it's not like I'm going to call the cops about product hiding, it's just not that big of a deal, and can be prevented if the store in keeping the store tidy and organized. Anybody that has been to Walmart knows that this is generally not the case, however.
I will say this. I would NEVER do this. Not because of it being criminal, but because I have too much pride, and my name is worth too much to be embarrassed over hiding Lego, and being questioned over it. Anyone with a professional career that actually has something on the line to lose, I guess is it worth the risk? I say no.