I think it is important, in this situation, to understand what everything is.
Your opponent's Reckless Scholar's activated ability is, "Tap: Target player draws a card, then discards a card." When this ability is activated, the owner of the trigger is your opponent. So, if he targets you with it, you can discard Obstinate Baloth for the desired effect since "a spell or ability controls causes you to discard" it.
Another way of putting it is that the game has very few way to check for whether you were forced to do something. I can't think of any replacement effects that would do this anyway.
Yeah, seems obvious in hindsight.
The "forced" effects I had in mind were when your opponent for example chooses a card from your hand to discard, or forces you to discard x cards where x is equal to or more than the number of cards in your hand. Situations where there is no choice in other words.
But like you said, the game doesn't incorporate a difference between whether it's forced or not.