People minute-to minute-speculating (day traders, hedge fund types etc) spend a ton of time trying to figure out what the BSDs are up to.  Which is why you have momentum indicators and the like.  People try to read more into the tape than just the price action.  Knowing who, how fast, size etc may (repeat may) mean something.

So if you are a big boy, people just seeing the broker you use buying heavy can be enough to start a rumor that big fund X is a buyer.  They then jump in and try to front run you.  So as a big player, you spend half your time trying to disguise your moves -- spoofing the others, lying to them etc.  These things I'd consider grey -- necessary evils because it is not a game of old maid and the rest of the market is not prevented from acting based on info they infer from other public info.  

Lying to a journalist to spook a market?  Getting pretty close to black but just how do you prosecute someone for saying "I hear on the 'vine that XYZ corp's new product will crush the IPod"  vs saying "I believe Apple is due for a correction because of stiffening competition from XYX corp".  Try to actually convict.  NFW. A seems dirty to me, but B is a rational reason for taking a position as a speculator.  

What the Enron boys did was clearly illegal (happened a bit in Europe in my day as well).  They specifically reported fake deals or lied about the price or did a deal which was later unwound in secret later in order to move the market marker services such as Platts in order to make a profit on some derivative instrument pricing off of the marker.

However, merely doing a series of deals in order to make the market move doesn't strike me as illegal.  If I wish to sell more than the market will take at say 100, then the market isn't 100.  It's where ever the next bid shows up.  If I only have to sell 100 in order to drop the price on 1000 I am buying elsewhere off of the market quotes have I broken any laws?  Or have I just pissed off the lords of fair play and the management of gutless operations that are only willing to trade off quotes determined by 22 year old journalism majors with 2 months experience reading market tea leaves or half assed futures exchange settles?