Yes, you could eat the losses for small things, however, people would write clients that actively try to double spend on every transaction meaning they pay for their things only maybe 25% of the time, and if such clients gain market share you are looking at eating a lot of losses.
If such things start happening, the methods of double spend checks would become more complicated, and fewer vendors will be willing to accept unconfirmed bitcoin transactions without ID and/or insurance. The fraudulent user is then in a digital arms race that he cannot win, and repeatedly doing these kinds of things is still going to get you caught eventually.