Mate, this was not a mistake and Lazlo himself doesn't consider it as the biggest mistake of his life. I have watched his interview and he said he's not regretting his actions. He has embedded his name in bitcoin as long as bitcoin lasts, as the first man to make a bitcoin transaction.
Also consider this;
As at when Lazlo bought his pizza, btc was worth about $0.004 and 10,000 of it should be about $41. So, it still easy for anyone to buy two pizzas with $41. Even if he didn't spend it for pizza, eventually he would have blown it on other things.