Computerized trading, high frequency traders, day trading, scalping, etc, are lubricants that grease the wheels of the market.
They don't by themselves cause liquidity void, vacuum, air-pockets, or flash crash if the old basic trading principles are followed and adhered to when adopting any new trading system by exchanges or government agencies, be it electronic, automated, and whatnot, namely: being FAIR, TRANSPARENT, and EFFICIENT.