But when you use high leverage every time you get stopped out a big chunk of your account is gone.
In your example of 10 contracts, a 5pt S&P stop would eat 8% of your 30K account. A 10 pt stop 16% of your account.
Three or four of those in a row and you will soon stop using leverage. Traders get longer losing streaks all the time, especially when using stops.
You make good points. Consecutive losses even while having positive expectancy would certainly hurt someone using levered assets. However, using proper risk management can certainly help to mitigate that, especially if you only take trades within certain risk parameters and are very disciplined about targets, etc.