If you posit that all a robo-advisor does is "decides which funds to invest in" for you, how are you putting too much trust into a computer? A target-date fund

If you posit that all a robo-advisor does is "decides which funds to invest in" for you, how are you putting too much trust into a computer? A target-date fund from Vanguard also makes allocation choices for you across US/international stocks/bonds; is the conclusion that you should always invest in the underlying asset class directly instead of trusting a fund/advisor/company to do it for you?