Surely, HFTs are the key player for spoofing? To play this game, you need to be able to pull your orders faster than people can execute on them. E.g. you see flow on one exchange, you pull on the other?
As I see it, the main problem with spoofing is that it distorts the market information. Any trader, human or machine, can look at the current order book and assume it is somewhat bona fide. Without that, exchanges are just a random draw (more than otherwise). Hence the appeal of dark pools (well, at one time) etc.
