Why does autofill on all the time?

I can't even play draft pick on Summoner's Rift because I might get support/ADC, both roles that I will never be good with. I can do top, jungle and mid, I hate everything about bot lane. Why can't you allow us to play the champions we want to play? This is one of the reasons I dislike this game and I almost never play it. I want to play Hecarim but I don't want to be stuck in a role that I have zero desire to play. Autofill needs to go away so I can play Summoner's Rift again.