But property laws are OK?

I just came up with a design for a machine that can save everyone time and money. I draw up the plans. You take a picture of the plans with a telescopic lens. You build the machine, sell it and profit. This is OK?

I build the machine and as I'm about to sell it at the market, you take it when I turn my back. You sell the machine and profit. This isn't OK?

So... what is the difference? In both cases you are hurting my ability to profit from my creation.