Look, we want markets to be as fair as possible, so once in a while (usually after a bust when politicians get out their lynch mob gear) we pass laws to require players in the market to play fair.
Most of these laws are great in the sense that they are good for the market's long term dynamism and good for "levelling the playing field".
But let's not kid ourselves, the playing field will never be completely levelled. If we want to get down to the level of questioning whether every big buy or sell is manipulative we're going to strangle liquidity in the name of fairness. There will always be games people play in markets and the optimal level of manipulation is not zero, so lets be grown up about it.
If in pursuit of eradicating every speck of manipulation we make life too difficult or expensive for people who want to trade our markets, the market will either dissappear or we will find US markets being made in London.
Lest you think this is a fairy tale, this DID happen when deep liquidity in Japanese futures momentarily migrated from Osaka to Singapore. Authorities eventually came to their senses and corrective measures brought liquidity back onshore over the decades.