Why do we have competing political parties?

The Founding Fathers opposed political parties, viewing them as "factions" dangerous to the public interest. But, they soon came into being because by uniting a group of like thinking people you have a greater chance of swaying voters and winning elections. Also, in the past political parties could vet candidates, but that value is largely gone today because anybody can run in primaries and the public, rather than the party, choose the candidates.