If you send a 1000 share buy order to the market, knowing that you're going to send 99 more of them throughout the day, you're making money (or at least losing less money) because of information that you have and your counterparties don't. And that kind of trading definitely has a negative effect on liquidity (almost the whole difficulty in market making is preferentially trading against people who aren't doing this). But this splitting of orders is universally viewed as "ok", and is how most large-volume trading is done these days.
The difference between this and insider trading is in who owns the information. Most people view the large-volume trader as doing something okay, because they own the information about their own future trading behavior. Insider trading is illegal not because it's unfair to trade on asymmetric information, but because you're trading on information that was stolen from the company. (This is why Mark Cuban didn't go to prison: a company gave him some insider information, but forgot to ask him not to trade on it; no stealing involved).
From this perspective, it makes sense to prosecute the original tipper, and anyone in the chain who knew (or should have known) that the information was stolen (by analogy to the crime of passing stolen goods), but not the guys at the end who were clueless about the scheme. (Although it might make sense to make them disgorge their trading profits.)