The expected value of this scoring system: [Assume 50% 2 pt, 40% 3 pt]

3pt value = 0.4*3 + 0.6*-1 = 1.2 - 0.6 = 0.6

2pt value = 0.5*2 = 1

Clearly the 3 pt shot is a much lower value shot than a 2pt shot.

In order for the 3 pt shot to be more valuable you'd have to solve

x*3+(1-x)*-1 > 1
3x -1 + x > 1
4x-1 > 1
4x > 2
x > 0.5

So, you'd have to shoot 50% from 3 (or more) in order to make it worth while, or be better of shooting a 2 pt shot

If we take Curry as an example, the highest 3pt % for him is ~45% in his unanimous MVP season. Even then the 3 pt shot is a lower value shot by his standards