That's fundamentally not the "logic that is keeping us in this two party system". That logic is the logic of understanding our current electoral system. The US electoral system as it currently stands will inevitably result in a two-party system. Sure you can change which two parties it is, that's happened several times, but without changing First Past The Post you're not going to get any other system.
That's exactly the flawed logic that is keeping us in this two party system. If we just vote for the candidate we support, neither Trump not Hillary would stand a chance.
The trouble with convincing people to actually do that is that most Americans feel the need to be on the winning side. "My vote is worthless unless it's for someone who can actually win."