Using symmetry to solve for electric flux I can't seem to figure out why wouldn't the flux be 0 through a disk in this instance:

These are two identical point charges. Wouldn't the scalar product with one be $cos\theta$ and the other $cos(180-\theta)$ so they cancel each other at each point? I think there's a simple concept I'm missing here and generally in calculating flux. 
 A: Imagine the setup flipped vertically. The charges swap positions and the surface stays in the same place because it is midway between the charges. The electric field everywhere is flipped vertically as well. However, because the charges are identical, swapping changes nothing, so the electric field everywhere must have stayed the same. Since the surface did not move during the flip, the electric field cannot not have changed after flipping. This can only be the case if the electric field in the surface has no component parallel to the normal vector, since that component would have been flipped. So, the electric field is perpendicular to the surface normal (parallel to the surface), and the flux is zero.
A: Take a look at net electric vector field in your case :

Gauss law states that electric flux through a closed surface is :
$$ \nabla \cdot \mathbf {E} ={\frac {\rho }{\varepsilon _{0}}} $$
This resolves along $x$ direction to :
$$ \frac {\partial \mathbf {E}_x}{\partial x} = {\frac {\rho }{\varepsilon _{0}}} $$
Of course we have no closed surface here, which is required for a full application of Gauss law, but partial application of it says that for an electric flux we must have electric field gradient. Your net $\mathbf {E}_x$ is zero, so electric flux along $x$ is zero too.
A: to electric field lines never intersect so , imagine electric field lines from the charges they are in same direction, due to similar nature of charges , so they would never intersect at surface so there cannot be any flux through it at all, also electric field along direction area vector would be 0 electric field would only exist at 90 degrees to area vector  (if there is field).
electric field concept was purely on basis of symmetry, as in the plane of surface its a mirror image so electric field would be equal but in opposite direction(due to similar charge) 
