*Credit XJaccounting
Like all trends, high frequency/algorithmic trading is bound to become a crowded field. You don't need to understand (most of) the fancy math and algorithms behind the professor's argument. Just think of it in terms of traditional arbitrage - the advantage fades once information turns from asymetrical to a more level field.
http://www.economics.harvard.edu/faculty/stein/files/
presidential-address-jf-final.pdf
For a less math oriented argument, please read Rick Bookstaber:
http://rick.bookstaber.com/2009/08/
not-with-bang-but-whimper-risk-from.html