As with most things in the universe of trading arbitrage is neither good, nor bad. It is simply a way to take profits from the markets. In some cases, you might even call it good since it maintains the efficient market by removing outliers. Others claim arbitrage is bad because it takes advantage of situations that shouldn't exist, or that may exist by mistake. At the end of the day traders are out there to make profits, and if they can do so by working with any imbalances that occur then that is simply part of the market process.