It doesn’t “raise barrier to entry”, it lowers it. Before HFT spreads on stocks were hell, imagine a quarter size spread. Now it’s mere pennies, fractions.

Also, for people who love computers, HFT is very exciting. Imagine a job where no optimization is too premature, where everything must be done to get the fastest possible speeds and push machines and software to physical limits. Very challenging and very fun. And the rewards are great!