This is an effort to stop FOM from introducing the Halo device on 2018 cars for many reasons.
1: It won't stop debris, such as the spring that hit Felipe Massa in 2009, from hitting the drivers as effectively as the aero shield would
2: It wouldn't be able to stand up to the force of a crash like the one that killed Jules Bianchi.
3: It's obstructive to the drivers in two ways.
a: It hinders the driver's exit from the car
b: It obstructs the driver's visibility
4: It it unpopular amongst a majority of teams and driver
5: It's ugly and could turn young fans off the sport. They don't want to watch a bunch of flip flops driving around!