That's bizarre. So let's say AAPL is trading at $120, and you put in a limit order to buy it at $110, then you should never be allowed to cancel it? How long does the order sit there for? What if AAPL's price goes up to $400 over the next few months, do you have to leave your limit order there forever?
I don't think fenollop means not withdraw it at all. He means after someone has said "I'll take that offer". At which point you can't withdraw it. So these people will make a loss of enough people take up their offers. This risk is mentioned in the article. It doesn't explain why "spoofing" is illegal though. It should be legal. They are trying to shift the market (so is everyone) through an action that exposes themselves to massive loses.
This system currently does not allow you to withdraw an offer once it has been matched. That is not what happened here.
The reason "spoofing" is illegal is because it gives a huge information advantage to one party that the other parties do not have. Similarly to insider trading. I have no opinion on whether those should be illegal, but if the basic premise of the market changes from "we assume everyone here wants to trade" to "this information is garbage", it will definitely have a negative impact on the price of the traded instruments.