Electrostatic forces can be blocked and opposite electrostatic charges can be used to neutralize or counteract another electrostatic charge thereby reducing or cancelling the effects of said field. Gravity cannot be neutralized by apply an opposite of the same field. If gravity were electrostatic/electromagnetic, then we would be able to develop antigravity devices. No one has ever been able to do such a thing. I think this alone destroys the notion that gravity is electrostatic in nature. Adding to this, we would be able to create artificial gravity by applying an electrostatic field if it were truly electric in nature. This is also not possible and there is no evidence that it could be possible. The idea that gravity is some other form of electronic field and force just doesn't hold up to practical experimentation. You can't block gravity. You can't neutralize it by applying an opposite like field. You can't create it by use of such a field. I'd say that effectively debunks the electrostatic theory of gravity.