Agents mainly do two things:
1. If selling they can put your house into MLS.
2. For buyers they can let you into a house.
Being able to do these things requires NAR membership, a state license, and other fees and cost real estate agents thousands per year. Also driving meetings clients at houses takes gas and time. Also your 6% commisiion is paying for all the other people that the agent spent gas and time on who did not buy a house.
Would you be willing to advertise in the news paper that your house is for sale and leave the doors unlocked so that random people could check it out?