The dichotomy of strict self control or a fall to the dark side makes no sense, because it says that force sensitives have to be Jedi, or be evil.
If you look at how the Sith work, they're not people who failed to control themselves, they're people who let their ambition rule them. They're an allegory for power, specifically political/ruling power, being a corrupting force. The Sith way of a ruthless quest for domination and power is the image of their corruption. It's also why they have to be iron fisted, because they make enemies everywhere. Which sets them up for their own fall from grace, usually at the hands of their own apprentice.
The Jedi on the other hand are the allegory for warrior monks, or more specifically the samurai. They give up everything to serve the greater good, to be mediators and peace keepers. Because they're supposed to lack desire for power and personal attachment, they're supposed to be incorruptible. Supposed to be, but aren't, because they can get over zealous and set themselves up for failure.
Still that leaves a lot of room between the two, people ranging from force sensitives who never have formal training, who may or may not find their own way. Sith and Jedi who lose faith in their master, or order, so they leave and exile them selves. To those who might have formal training, but go of to pursue their own interests and fortunes. Nothing says that one has to pick one order, or the other, except for the Jedi and Sith themselves. The reason you wouldn't see many force sensitives identified is a pretty simple reason, they'd keep their heads down, because they'd be pestered by the Jedi to follow the Jedi way, or would have a Sith attempt to recruit, or kill them.