The same way insider trading is banned. It is impossible to prevent 100% of insider information being involved in some trades but you can prosecute people who can be proven to have made trades on insider information.
How do you "ban" a fast connection? How do you even define a fast(er) connection?
If I'm the CFO of company X I have an unfair advantage when it comes to making trades minutes before the quarterly results are release for my company.
This would be very similar to insider trading in that there is going to be a grey area where it would be hard to prove that the intent was to undercut someone else but having the regulation there would at least curtail this practice somewhat.