I see your point and it is a good one!
Most people that step out into the road in front of me on my commute are doing the 'ipod shuffle', distracted by text or talking about what they are going to have for dinner. So it isn't as if they are distracted by anything really significant and in some way that is where the danger is - an assumption they can multi-task whilst crossing the road. If they were interrupted by someone calling to say they had won the lottery etc. then they probably would stop in their tracks and not attempt to cross the road there and then.
When I found the wallet the other day I did think whether anyone had seen me and I did think about whether there was CCTV and whether I could get caught had I just taken the money. However I quickly decided that I was going to try and return the wallet. I made a few paces up the road before turning back and going to the corner shop to see if they recognised the guy in the travelcard photo. I was distracted, no question about it, and, had I needed to have crossed a road then I might not have had my wits about me.
So, what would have happened had I decided to take the money? Rather than think about whether I had been seen I would have had to actually check every bit of street furniture for CCTV and every window overlooking me. I would have had to surreptitiously put the wallet in a pocket and gone through the thought process of where I was to dispose of it etc. Maybe, as a result, I would have been extra careful on the road.
However, I believe that cheating/stealing/doing wrong poses an abnormal and detrimental strain to thinking. By analogy, one of my Scrabble playing friends has this habit of cheating. He is a journalist with a considerable vocabulary, with pride to match. Therefore he has to win. However, the rest of us know that he sometimes does things with the letters bag and sometimes we choose to turn a blind eye. The added strain of cheating and not getting caught affects his game meaning that he puts himself at a competitive disadvantage. He can have a rack full of 'Q's and 'Z's and miss a seven letter triple word score word like 'quizzed' because he is more focused on trying to get a 'U' from the bag when there is a perfectly good one on the board already.
To conclude, it is the element of deceit.