You generally would not resist it, you would float your opponent, or put your opponent in a hole. This is what the aikido waza look like to me. You get underneath or unbalance your partner, then put them into a direction they are weak.
Martially its better to not have force on force on the same angle unless you can generate more than the other guy.
As for athletics, it is not my experience that most people can innately do a ground path. Sure they can do it once they are shown, but that isn't their initial reaction.
I agree with this. Ability to resist a push stops making sense at some point.
But Dan also convinced me that you need it to go further. Can one really achieve the bold part without this ability if the opponent does not cooperate?